American Lucas Glover survived late charges from Phil Mickelson and David Duval to clinch the rain-hit 109th US Open at Bethpage on Monday.
Glover claimed his maiden major by two shots from world number two Mickelson, former world number one Duval and third-round leader Ricky Barnes.
England's Ross Fisher was close for much of the final round but ended three back for his best major finish.
Tiger Woods threatened but ended four strokes behind Glover at level par.
The tournament was wide open for much of the final day as Barnes, who held a six-shot lead at one stage during the third round, and Glover came back to the pack after starting the day tied for the lead at seven under, five shots clear.
As Tour rookie Barnes fell away early on, Mickelson twice joined Glover in the lead, once with an eagle on the 13th and then again as his compatriot three-putted on 15, his only three-putt of the week.
But Mickelson slipped back with a bogey on 17 and Duval, who had amassed a triple-bogey six on the 3rd, fought back to join Glover out in front with a third straight birdie on 16.
Duval, ranked 882 in the world at the start of the week, also dropped a shot on 17 and Glover picked up a shot of his own to take a two-shot lead into the final two holes.
The 29-year-old, who won his solitary PGA Tour title in 2005, carded careful pars at 17 and 18 for a 73 and an unlikely victory.
"It was a test of patience," he said. "It was tough, we got the full value of the course. But the golf course played fantastic and it was just hard.
"The birdie at 16 was [also] huge. I heard some roars ahead and know it was important."
Glover, ranked 71 in the world before the event, was second at Charlotte last month for his best PGA showing of the year but had missed the cut in his three prior US Open appearances. His best finish in 11 previous majors was tied 20th at the 2007 Masters.
"I guess if I can win this one, I should be able to play all right every week," Glover said. "It will definitely be a big confidence boost."
It was an emotional five days. I want to win this tournament badly
Three-time major winner Mickelson, playing in his last event before wife Amy begins breast cancer treatment next month, carded a round of 70 to endure the heartbreak of a record fifth runner-up finish at the US Open and second at Bethpage after 2002.
"It was a lot of ups and downs for me, fighting to get back in it," said the 39-year-old left-hander, who was roared on by the adoring New York crowds.
"It was an emotional five days. I want to win this tournament badly. I feel I will have more chances."
Duval, the 2001 Open champion who has been in the golfing wilderness for much of the last eight years, collected his first top-10 finish in any tournament since 2002 with a closing 71.
"I'm pleased with how I played but disappointed at where I finished. I came here to win," Duval said. "It may be arrogance but it's where I feel like I belong."
Barnes, the 2002 US Amateur champion, set a new US Open 36-hole scoring record of 132 and reached 11 under during the third round, but he struggled with his game for much of the day in the final group with Glover and carded a 76.
Fisher, the world number 29, struck a superb eagle putt at the 13th hole to move three under and within one of the lead but bogeys on 15 and 17 took him to a round of 72 and killed his chances of becoming the first Briton to win the US Open since Tony Jacklin in 1970.
"It's something I will never forget," said the 28-year-old, who learned his golf at Wentworth. "This is only my second US Open. But what an experience."
World number one Woods, who has never won a major when not at least sharing the 54-hole lead, failed in his bid to create more golf history.
He was aiming for a record-equalling fourth US Open crown and to become the first man to defend all four major titles by winning his 15th major.
Woods, who made the cut by one and was 14 strokes adrift at one stage during the second round, edged closer to the top as the leaders faltered, while back-to-back birdies at 13 and 14 gave him hope.
But his late charge petered out with a bogey at the 15th and missed birdie putts on 16 and 17 as he carded 69 to finish tied sixth with Soren Hansen and Hunter Mahan.
"I gave myself so many chances and made nothing," said Woods.
Sweden's Henrik Stenson finished on one over, while Northern Ireland's Rory McIlory made a move with a 68 to end two over alongside Spain's Sergio Garcia.
The Monday finish, caused by torrential rain and waterlogging on Thursday and Saturday evening halting play, was the first time a US Open has overrun in regulation play since Larry Nelson won at Oakmont in 1983.