Wyndham Clark began Sunday's final round of the US Open with a six-stroke lead in search of a wire-to-wire victory while playing partner Scottie Scheffler chased a historic fightback triumph.
The Americans teed off in the final pairing at windy Shinnecock Hills with Clark, the 2023 US Open champion, leading on seven-under par.
Top-ranked Scheffler, a four-time major winner, was trying to complete a career Grand Slam on his 30th birthday.
Scheffler was tied for second on one-under with South Korean Tom Kim, England's Tommy Fleetwood and fellow Americans Sahith Theegala, Sam Stevens and Sam Burns as the closing drama began to unfold over the fast greens and dense rough of the links-style layout.
Clark could become only the ninth wire-to-wire US Open winner and the first since Germany's Martin Kaymer at Pinehurst in 2014.
The only golfer to lead a major by six or more strokes entering the final round and lose was Greg Norman at the 1996 Masters.
Arnold Palmer made the greatest final-round victory comeback in US Open history, rallying from seven down over the last 18 holes in 1960 at Cherry Hills.
Clark, 32, won his fourth PGA Tour title last month in Texas and said he wants to win the US Open to help erase the bad feelings over smashing a locker at Oakmont after missing the cut in last year's US Open.
The winner will take home a record $4.5 million top prize from a $22.5 million purse, matching the highest in major golf.
Scheffler, however, would capture far more should he overcome Clark for his first US Open title.
Scheffler would become only the seventh player to complete the career Grand Slam, the first since Rory McIlroy did it last year by winning the Masters.
Others with a victory in all four majors are Tiger Woods, Jack Nicklaus, Gary Player, Ben Hogan and Gene Sarazen.
It would mark the fifth career major title for Scheffler, who won the 2022 and 2024 Masters and last year's PGA Championship and British Open.
This year, Scheffler won his season opener in California desert and had runner-up finishes at the Masters, Heritage and Doral tournaments.
Kim, a three-time PGA Tour winner, could take a first major title on his 24th birthday. He shared second at the 2023 British Open for his best finish in 16 prior major starts.
Theegala, 28, won his only PGA Tour title at the 2023 Fortinet Championship. His best finish in 14 prior major starts was ninth in his 2023 Masters debut.
Stevens, 29 and in only his eighth major start, has never won a PGA Tour event but was second last year at Torrey Pines and the 3M Open and in the 2024 Texas Open.
Sunday's early groups raised hopes for low scores with Sweden's Ludvig Aberg and American Peter Uihlein each firing four-under 66.