On a back nine filled with double bogeys by so many contenders and a shocking meltdown by defending champion Bryson DeChambeau, Oosthuizen was the last to fall.
Trailing by one shot, Oosthuizen drove into the canyon left of the 17th fairway for a bogey that left him two shots behind, and then he missed the fairway on the par-5 18th that kept him from going for the green for a look at eagle to force a playoff.
He settled for a birdie and a 71. It was his second straight runner-up in a major, and his sixth silver medal since he won the British Open in 2010 at St. Andrews.
Only two weeks ago, Rahm was on the cusp of another big win. He had a six-shot lead at the Memorial after 54 holes, only to be notified as he walked off the 18th green at Muirfield Village that he had a positive COVID-19 test and had to withdraw.
Worse yet, his parents had flown in from Spain to see their new grandson, and Rahm was in self-isolation and couldn't be there for a special moment.
Sunday made up for it. His parents were at Torrey Pines to witness a world-class performance capped off by one of the great finishes in U.S. Open history.
Rahm finished at 5-under 278 for his 12th victory worldwide. The first one was at Torrey Pines four years ago when he holed a 50-foot eagle putt on the 18th.
- AP