Pettersen, who enters her sophomore year at Auburn High School in Rockford in the fall, finished off the 54-hole competition with a 66 and won the title by five strokes. She posed an 8-under-par 208 total to become the youngest-ever winner of the 21-year old championship.

“I came to be low amateur, but this means a lot,’’ said Pettersen, “mainly because I broke my personal records. I’ve shot 67s and 68s before, and now I finally shot a 66. I finally made five birdies in a row. I had four in a row before.’’

The five straight birds came at the end of her round and left playing partner Chelsea Harris of Normal dazed.

“I got outplayed,’’ said Harris, who was low pro in the event that started with 68 players on Monday. “She’s a great player to make five birdies. She was a machine.’’

Pettersen and Harris, the assistant women’s coach at Illinois State, started the final round in a three-way tie for the lead with Symetra Tour player Ember Schuldt of Sterling. Schuldt’s late charge fizzled when she missed birdie putts from five feet at Nos. 14 and 15. She also missed a good birdie chance at No. 18 after putting her second shot to the par-5 on the back fringe of the green.

That allowed Harris, who ended in a tie for second with University of Wisconsin amateur Brooke Ferrell, to edge Schuldt for the $5,000 check awarded the low pro.

Otherwise, the show belonged to Pettersen who had her 9-year old sister Isabella as her caddie in the final round. Their mother was on Madasyn’s bag for the first two rounds while Isabella was playing in her own tournament.

Madasyn entered the ISO when she was 11 but failed to make the 36-hole cut. She didn’t return until this year and dominated from the outset. She either led or was tied for the lead after all three rounds.

Though the Pettersen-Harris pairing lagged two holes behind the next-to-the-last group, the best golf came from the last finishers. Pettersen’s charge to the title started at No. 14 – a 190-yard par-3 over water that marks the beginning of the Kelpie’s Corner stretch of holes. She hit that green with a 5-iron and made the first of her five straight birdies from 15 feet.

She hit the par-5 15th with an 8-iron from 200 yards and two-putted to keep the birdie streak going and followed with putts of 15 feet at No. 16, 12 feet at No.17 and 15 feet at No. 18.

“I was just focusing on closing it out,’’ said Pettersen, who found her putting magic a few months ago.

“One day this spring I woke up and decided I wanted to putt like Jordan Spieth,’’ she said. “I copied his putting grip, but I kind of do my own thing.’’

Pettersen isn’t sure if she’ll play high school golf again, but she does take off Friday for the PGA Junior Girls Championship in Texas.

David Cooke’s victory in the 66th Illinois Open was a run-away. His five-shot victory at Royal Melbourne, in Long Grove, was the biggest since Gary Hallberg’s triumph in 1977.

Though the tourney lacked suspense, it was loaded with emotion and another historical touch. Cooke was the first amateur to win the title since Brad Benjamin in 2009. Hallberg, who went on to a solid career as a touring pro, was also an amateur when he won at Elgin Country Club 38 years ago.

Cooke’s win, though, was more about family than it was about history. Last Dec. 23 he lost his younger brother Chad, a 20-year old basketball player at Charleston Southern. He passed away from an apparent heart disorder while playing in a pickup basketball game.

“He was a strong encourager of everybody,’’ said David Cookie. “I knew he’d want me to keep playing. I tried to focus on that and think about positives. I have great memories of my little brother. I wish more than anything that we could have him back.’’

Chad was occasionally David’s caddie in tournaments. His older brother Jay, 34, came from South Carolina to work as David’s caddie in the Illinois Open and they were followed by their parents, grandparents and other family members and friends who walked with them in the final round.

“It was an emotional win,’’ said Cooke, who will enter his senior year at North Carolina State in the fall. “It’s been a rough last year, and it meant a lot to me and my older brother that everyone was here.’’

Cooke grew up in Bolingbrook, and his family moved to Lisle several months ago. He had never led a tournament over night until he shared a one-stroke lead with Brad Marek of Arlington Heights heading into Wednesday’s final round of the Illinois Open.

“There were nerves on the first tee,’’ Cooke admitted, but they went away quickly when Cooke hit a pitching wedge from 144 yards to six feet and then rolled in a putt for eagle at No. 1. He made birdies on the next three holes as well and coasted from there.

Cooke had been in the next-to-the-last group in the final round of the Illinois Open in 2012 and 2013 but fizzled down the stretch. He didn’t play in the event last year and basically had only Vince India, a Web.com Tour player from Deerfield, as a challenger in the final round.

“David played great,’’ said India. “I certainly played fine. I shot 5-under, but what are you going to do?’’

Cooke shot 63 on Wednesday and finished at 16-under-par 199 for the 54 holes. India shot 67 but did claim the $12,500 check for being low pro.

“This win was a big motivator for me,’’ said Cooke. “It showed me I could compete with pros. It helps me know that I’m on the right path.’’

Cooke’s round wasn’t the best of the day. Early starter Matt Weber, an Indiana University sophomore from Hinsdale, posted a 62 to tie the course record but he finished in a tie for 13th place.

Monday turned out a big day for the golfers at Conway Farms – but an even bigger one for David Lawrence. The Moline golfer shot a 9-under-par 62 at Royal Melbourne in Long Grove. That’s the lowest round in the 66-year history of the Illinois Open.

Lawrence, who has been playing golf’s mini-tour since attending Eastern Illinois, wasn’t the whole show on the first day of the 54-hole competition. Three players shot 66, among them Conway Farms head professional Matt Slowinski. His hot round came on the same day that Zach Johnson won the British Open in Scotland. Johnson also has ties to the Lake Forest club, having won the PGA Tour’s BMW Championship there in 2013.

Johnson’s victory at St. Andrews was good news for Slowinski, with the BMW Championship returning to Conway Farms in September.

“I’m glad he won it. It’ll be good for our event as well,’’ said Slowinski, who had a strange round, despite the good result.

“You never feel good hitting a provisional on the first hole,’’ he said, “but I wound up making a 15-footer for bogey and got the momentum going from there.’’

The momentum reached a crescendo on his last shot, when Slowinski holed a gap wedge from 125 yards for eagle to finish off his round. That left him in a three-way tie for second with amateur Nick Hardy of Northbrook and Deerfield’s Vince India, who has spent the last two seasons on the Web.com Tour.

With 258 starters – 151 of them amateurs, this is the biggest-ever Illinois Open. The Illinois PGA changed the format this year, boosting the field from last year’s 156 and going to two sites for the 54-hole finals. Half the field played at Royal Melbourne, in Long Grove, and the other half at Hawthorn Woods Country Club.

“I like (the new format),’’ said Slowinski. “It’s good to see more people in the field, and it’ll make the event better.’’

Slowinski opened his title bid at Royal Melbourne and plays at Hawthorn Woods on Tuesday. That was encouraging for him because his best Illinois Open was a tie for fourth when the event was contested at that course from 2008-11. Hardy and India also posted their low scores at Royal Melbourne.

Hardy is in the midst of a torrid schedule. He finished third in the Illinois State Amateur last week at Panther Creek, in Springfield. After the Illinois Open he has the Western Amateur at Rich Harvest, in Sugar Grove, and the U.S. Amateur, at Olympia Fields, on his August schedule.

The field will be cut to the low 70 and ties (up from the 50 and ties from previous years) after Tuesday’s rounds at both courses. The final 18 will be at Royal Melbourne on Wednesday.

SPRINGFIELD, IL. – A year ago Naperville’s Ray Knoll and Northbrook’s Nick Hardy battled through four playoff holes before Knoll won the Illinois State Amateur title. Knoll couldn’t repeat this year, and Hardy didn’t win, either, but nobody played better than those two during this year’s final round at Panther Creek Country Club on Thursday. They were spectacular.

Tee-K Kelly, a Medinah member from Wheaton, won his second Illinois Am title in a three-hole aggregate score playoff with 18-year old Conor Dore of Chicago, but that result was somewhat overshadowed by the record rounds posted by college stars Knoll (Iowa) and Hardy (Illinois).

Hardy matched the course record of 6-under-par 65 but wound up third. For the final 18 holes Knoll was even better. He posted what’s believed to be the lowest round in the 85-year history of the Illinois Am – an 8-under 63 – and it included what’s believed to be the first albatross in the event’s history as well. Chicago District Golf Assn. officials couldn’t confirm the apparent milestones because much of the tournament data was lost in weather-related damage several years ago.

Knoll, who enters his junior year at Iowa in the fall, saw his title defense evaporate after shooting a 75 in the morning 18 holes of the 36-hole final day. Making six birdies in the first 11 holes in the afternoon, all from the four to 10-foot range, Knoll climbed the leaderboard but saved his best for No. 15, a 576-yard par-5.

“Going to the last round I knew I didn’t have a chance to win, but I was playing good and just tried to be aggressive,’’ he said. So, at No. 15 he blasted a “perfect’’ drive, then studied the possibility of going for the green with his second.

“I didn’t know what my yardage was because my rangefinder died when I was on the 10th hole,’’ he said. “I stepped it off from the 200-yard marker and found the yardage was 267 yards plus three more to the pin. I hit a high draw with my 3-wood and swung a little harder because that distance was a little out of my range.’’

Well, actually it wasn’t. His ball landed on the front of the green, bounced once and rolled into the hole. It was his second albatross, the first coming on a 6-iron shot from 191 yards while playing an informal round with his father at Hickory Ridge in Carbondale.

This one elevated Knoll to under-par status for the tournament and into a tie for sixth place. He wasn’t close to the front-runners — Dore, who enters his freshman year at Southern Illinois-Edwardsville in the fall, and Kelly, who won the title for the first time in 2013. They finished the regulation 72 holes at 9-under-par 275.

Dore, who ruled the Chicago Public League for three years while at Whitney Young, made three costly bogeys down the stretch – the first at No. 17 in regulation and the last two in the final two holes of the playoff. That made Kelly, a senior-to-be at Ohio State, the champion off his three pars in the extra session.

SILVIS, IL. – Bring on the British Open. Jordan Spieth is more than ready to claim the third leg of what could be the first modern day golf Grand Slam.

The 21-year old Masters and U.S. Open champion won the John Deere Classic for the second time without his best stuff on Sunday, then boarded a jet with a batch of other players for this week’s third major championship of the year at storied St. Andrews in Scotland.

Spieth started the final round of the JDC with a two-stroke lead but trailed by four with six holes to go. Tom Gillis, a 46-year old journeyman without a win in 171 starts on the PGA Tour, got hot early and posted a 7-under-par 64. That made him the clubhouse leader at 20-under 264 for the regulation 72 holes.

Gillis, who played four groups in front of Spieth, made a costly bogey at the 16th and Spieth made three birdies to force a playoff. The extra session went two holes, Spieth winning with a par after Gillis hit a tee shot into the right rough and his second into a pond on the left side of the fairway.

Spieth started the tournament with a par-71 round, showing rust after a two-week layoff. He was hot in rounds two and three, shooting 64 and 61, then cooled off again on Sunday.

“I didn’t have my best for the first 12 holes or so, but it’s very satisfying to have stretches like that and still come out with the win,’’ he said. “This gives me a lot of momentum to draw on.’’

Sunday wasn’t just a duel between Gillis and Spieth. Danny Lee, winner of the Greenbrier Classic – last week’s PGA Tour stop, and hometown favorite Zach Johnson also were in the hunt. Unusual circumstances derailed both.

Lee went brain-dead at the fourth hole. With the course soggy from heavy rains on Saturday, the lift, clean and place rule was invoked. That wasn’t the case on Sunday. Lee picked up his ball “without just thinking.’’ His caddie gave him the bad news – a one-stroke penalty that eventually kept him out of the playoff.

Johnson might have been in the playoff as well. He was lining up a birdie putt on the No. 16 green when what sounded like a gunshot forced him to jump back. It apparently came from a pontoon boat on the nearby Rock River and security officers quickly rushed to the scene.

“I don’t know if it was a backfire from a boat or a firecracker or what,’’ said Johnson, who was clearly shaken by the incident but didn’t blame his finish on it. He left his 35-foot birdie putt two feet short but salvaged par and wound up tied for third with Lee, one stroke out of the playoff.

Gillis was on the brink of being the latest first-time champion at the JDC – there have been seven just since 2000. He carried a No. 643 world ranking into the week and was No. 194 in the FedEx Cup standings and No. 199 on the PGA Tour’s season money list. In finishing second he earned a seat on the jet to the British Open.

“The week was a success overall,’’ he said. “I haven’t shown a whole lot of form coming back from shoulder surgery. I missed four months this year, and you start to wonder how much more is there. After what I saw this week I’d say maybe I’ve got some time left.’’

Spieth has much more of it, of course. He left for St. Andrews as the sixth player to have won the first two majors championship of the year. The only Grand Slam in golf history was by Bobby Jones in 1930, but his four wins were in different tournaments – the U.S. Amateur and British Amateur replacing the Masters and PGA Championship, which are included now. Jones’ other wins were in the U.S. Open and British Open.

“I’ve heard St. Andrews is playing softer than usual, which is kind of nice for having come from here,’’ said Spieth. He has been at St. Andrews only once, for two days over three years ago. He loved the setting, but was widely criticized the last three weeks for not skipping the JDC to allow for more preparation in Europe with such a big title on the line.

“I really didn’t care about that,’’ he said. “I came here for a reason, and we accomplished that reason. Certainly we have some momentum going into next week.’’