The Spaniard, ranked second in the world behind Johnson, was in the right rough off the tee at the first playoff hole, the 18th at Olympia Fields near Chicago. His second shot rolled to the back of the green, leaving him what could have been a tough two-putt for par.
Even he could not believe what he did. "Never did I think I'd be making another 50-, 60-footer – couple of breaks in there, too – to end up winning it," said Rahm, who gave a roaring fist pump as the putt dropped.
Johnson's tee shot was also off course but ricocheted off a tree to settle in the fairway. DJ found the middle of the green, but after Rahm's miraculous birdie effort, Johnson's birdie attempt settled inches from the cup.
Johnson managed to get in a 43-foot birdie at the same hole to force the playoff, joining Rahm on four-under-par 276 in the second event of the US tour's FedEx Cup playoffs. Rahm had powered to the top of the leader board with six birdies in an impressive six-under-par 64 – the lowest round of the week.
"I still can't believe what just happened, what happened the last hour of play," Rahm said. "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."
Johnson's solo second place means he'll stay atop the rankings.
Rahm was tied for sixth starting the day after a third round marred by a bad mistake at the fifth hole, where he absentmindedly picked up his ball on the green without marking it and was assessed a penalty.
"Once I teed off today, in the good weather and how I started striping it the first few holes, I knew I had a chance," said Rahm, who claimed his fifth tour title and his second in his last five starts. "Obviously I knew I needed to make birdie to get into the playoff," he said.
"I played an unbelievable putt, got in the playoff and then Jon made an even more ridiculous putt on top of me." John Rahm is sure to remember this day for a long while to come.