On a dramatic final day at Torrey Pines, defending champion Bryson DeChambeau had his nose in front at the turn before capitulating in spectacular fashion on the back nine, as did 2011 winner Rory McIlroy after he’d put himself in a promising position as the season’s third major hit the business end.
Holding a two-shot lead with eight holes to play on the California coast, South African Louis Oosthuizen looked to be in the driving seat in his bid to add to his 2010 Open Championship win at St Andrews, but Rahm had different ideas.
On the same course where he’d landed his maiden PGA Tour win in the Farmers Insurance Open four years ago, the 26-year-old finished birdie-birdie, rolling in left-to-right putts on both occasions.
There was a 10-foot break in the first one from 24 feet, with a huge fist pump from Rahm showing what that meant, as was the case when he celebrated in similar fashion as an 18-footer also dropped at the last.
The late burst gave him a closing 67, having earlier made three birdies, including one at the par-5 ninth, where he made the most of a lucky break as an errant tee shot somehow avoided going out of bounds.
Rahm’s six-under 278 total left Oosthuizen, who was playing in the final group, needing a birdie over the closing holes to force a play-off in the USGA event, but, yet again, he had to settle for second best in one of the game’s big events.
One behind Rahm, Oosthhuizen’s tee shot at the 17th was too tight and kicked into a hazard, ending his title hopes as he finished runner-up in this event for a second time and a fifth time in total in the majors.
"I’m a big believer in karma and, after what happened a couple of weeks ago, I stayed really positive knowing big things were coming,” said Rahm as he savoured becoming the first Spaniard to win this event.
"I didn’t know what it was going to be, but I knew we were coming to a special place, I knew I got my breakthrough win here and it’s very special place for my family.
"The fact my parents were able to come (from Spain), the fact I got out of my Covid protocol early, I just felt the starts were alinging and I knew my best golf was to come.
"I have a hard time explaining what just happened because I can’t believe I made the last two putts and I’m the first Spanish player to win the US Open. This was definitely for Seve [Ballesteros] as I know that he wanted to win this one most of all.”
American Harris English, who had closed with a 68, finished third on three-under, one ahead of Italian Guido Migliozzi (68), two time-champion Brooks Koepka (69) and last year’s US PGA champion Collin Morikawa (70).
McIlroy, who had the wind taken out of his sails by a three-putt at the 11th then getting an awful plugged lie in a greenside bunker at the next, had to settle for a tie for seventh as a closing 73 left him on one-under.
As for DeChambeau, a horror back nine that included a quadruple-bogey 8 at the 17th saw him close with a 77 to go from leading to end up in a tie for 26th on three-over.
Bob MacIntyre (73) tied for 35th on five-over after making it six cuts in six major appearances, finishing six shots ahead of local favourite and fellow left-hander Phil Mickelson (75).