Rahm was on the range, preparing for an unexpected playoff when Dustin Johnson rolled in a 45-foot birdie putt down the ridge. Moments later, Rahm faced an even longer and much more difficult putt on the 18th - just outside 65 feet that needed to be played at nearly a 90-degree angle to the top of the ridge.
From there, it was almost a replay of Johnson's putt as it headed down the slope, kissed off the pin and disappeared into the cup. "I still can't believe what just happened," Rahm said. Neither could Johnson, who really wanted his second straight victory.
He could only laugh, at his putt and Rahm's winner. "I played an unbelievable putt, got in the playoff and then Jon made an even more ridiculous putt on top of me," said Johnson, who at least kept his No. 1 ranking in the world and in the FedEx Cup.
The putts overshadowed a command performance by Rahm, who closed with a 66-64 weekend on an Olympia Fields course that played like the toughest test in golf.
Spectacular golf all round
Rahm's only bogey on the weekend came on the fifth hole on Saturday when he spaced out bizarrely picked up his golf ball from the green without marking it.
There was the 6-iron from 218 yards for his third shot on the par-5 15th after his tee shot went into the trees and barely came out, setting up a key birdie. There was also his spectacular 30-foot birdie putt on the par-3 16th for a two-shot lead.
However, Johnson it erased with two birdies of his own. "That stretch of waiting for DJ, him making the putt, going in the playoff, me making the putt, then trying to stay mentally in it just in case he made the last putt, it's been a roller coaster, but so much fun," Rahm said.
All he could think about on the 18th green in the playoff was finding a way to get to the next hole, knowing he had a putt from one end of the green to the other and Johnson had a 30-footer. And then it was over. Rahm won for the second time this year, and for the 11th time worldwide in his four years as a pro.
Tiger Woods missed all the action. He made double bogey on his 17th hole for a 71, making this the first time he was over par in all four rounds of a tournament since the Bridgestone Invitational in 2010. Woods failed to reach the Tour Championship for the second straight year.
He now gets two weeks off before the U.S. Open at Winged Foot, and Olympia Fields proved to be a good test for that. "I think we all want the flashy finish, maybe not the stress that comes with it," Rahm said. "But I set out with myself to enjoy even the uncomfortable moments we had out there today.
And man, it was fun." The course that all week felt like a U.S. Open delivered the kind of excitement typical of the Masters.