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In chaos theory, the butterfly effect refers to the notion that a simple action — such as the flapping of a butterfly’s wings — can have vast consequences, such as an eventual hurricane halfway around the world.

Perhaps a butterfly also changed the course of the Western Amateur Championship match-play final on Saturday at Knollwood Club in Lake Forest.

Florida sophomore and stroke-play medalist Sam Horsfield had a two-hole lead against Illinois’ Dylan Meyer and was standing over his par putt on the sixth hole when a butterfly flew across the green and right past his face.

Horsfield stepped away from his line, approached again, then watched as his 10-foot putt lipped out. He conceded the hole to Meyer, a junior who would have had a tap-in for par.

Meyer won the next hole, then went ahead for good on the par-5 10th en route to a 3-and-1 victory and the Western Amateur title.

Meyer joins a distinguished list of Western Amateur champions, including Jack Nicklaus, Tiger Woods, Phil Mickelson, Andy North, Curtis Strange and Ben Crenshaw. The marathon tournament features eight rounds of golf over five days, including two rounds apiece the final three days.

“I was rolling the rock this week, as Coach (Mike Small of Illinois) likes to say,” Meyer said. “Putts were falling. It was just my week this week.”

Meyer had the backing of a pro-Illinois crowd, but had to contend with Horsfield’s immense power off the tee. Horsfield’s drives routinely topped 300 yards and occasionally approached 350, drawing hushed oohs and aahs from the gallery of about 150 spectators.

Meyer frequently found the rough and sand, but made up for it with a series of impeccable approach shots. Horsfield was solid tee to green, but watched as putt after putt missed by inches.

Meyer protected his one-hole lead with a 20-foot uphill putt from the fringe to save par at the 11th. It marked his third par save in four chances after finding a bunker.

“I know my place, I know how I am, I know my stature,” said the 5-foot-10, 140-pound Meyer. “I’m just going to stick to my game. I’m not going to be a Jason Day, I’m not going to be a Dustin Johnson. I want to be a Zach Johnson. I’m gonna short-game-to-death … the golf course.”

Horsfield, of Manchester, England, earned medalist honors by nine strokes and entered the match-play Sweet 16 as the top seed. Meyer, from Evansville, Ind., finished stroke play in a six-way tie for 12th and survived a playoff to earn the 15 seed. He beat the second, seventh, 14th and first seeds to claim the title. He topped Arlington Heights native and Buffalo Grove alum Doug Ghim in the quarterfinals.

Among Meyer’s closest friends is Northbrook native Nick Hardy, who also advanced to match play before falling in the first round. Meyer stayed at Hardy’s home all week and found his short game could outduel many of the tournament’s heaviest hitters.

Meyer’s previous top finish in a national tournament was second in the 2013 Western Junior. He clinched the victory on the par-3 17th when Horsfield conceded following his third shot.

“It was just a couple of tough breaks here and there, a couple of tough putts,” Horsfield said. “It hurts right now. I’ve never really felt like this about a tournament, but I’m excited about where my game’s at. This is one of the best fields in amateur golf.”

Meyer, Horsfield, Hardy and Ghim all have qualified for the U.S. Amateur, which begins Monday, Aug. 15, at Oakland Hills Country Club in suburban Detroit. Beyond that, Meyer looks forward to returning to campus with Hardy in the fall, where they will be the unquestioned leaders of one of the nation’s best college golf teams.

“Me and Nick both know that we have to step up and fill in those shoes,” Meyer said of replacing Illinois’ graduated seniors. “With the way Nick played in the Illinois Am (he won by 10 shots at 28-under-par) and the way I played here, it’s a really good sign of what we’ve got.”

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