Phil Mickelson held his nerve to win the rain-delayed USPGA at Baltusrol by a single shot after a final-round 72.
The American led by one shot when play resumed on Monday after Sunday's action had been suspended because of storms.
He bogeyed the 16th to move back to three under alongside Australian Steve Elkington and Dane Thomas Bjorn.
But with his rivals in the clubhouse, he played a delightful chip at the 18th to set up a two-foot birdie putt which he holed to win his second major title.
The 2004 Masters champion resumed on the 14th on Monday with Bjorn and Elkington just a shot back and Tiger Woods the clubhouse leader at two under.
Mickelson, 35, began solidly, sinking his par putt at the 14th to put the pressure back on his rivals.
Bjorn slipped briefly out of contention when he bogeyed the 15th but the Dane recovered well to go back to three under after a birdie at the 17th.
Bjorn missed a crucial birdie opportunity at the 18th
The pressure rose on Mickelson when he bunkered his tee-shot at the 16th and he ended with a bogey but again he managed to keep his cool.
Elkington, who won this tournament 10 years ago, played solidly over the final holes but could not get the breaks which might have given him another major title.
Bjorn, bidding to be the first European major winner since Paul Lawrie in 1999, then had a glorious chance to take the outright lead at the 554-yard par five 18th but his birdie putt agonisingly lipped out.
And with the tournament reaching its climax, Mickelson birdied his last hole to give him a dramatic victory.
The final-day drama left world number one Tiger Woods, the overnight clubhouse leader on two under, tied for fourth place with 1995 champion Davis Love.
Woods, who only just survived the cut, had been bidding to become the first player to win three majors in a season on two occasions.
Mickelson and compatriot Love had taken a one-shot lead into the final round.
Mickelson marched into a three-stroke advantage when he parred the first three holes before sinking a six-foot birdie on the fourth.
In contrast, Love had a hat-trick of bogeys from the third and suddenly it was Elkington who became the greatest challenger to the left-hander.
The Australian had rolled in a 15-footer on the ninth to turn in a one-under 33.
However, he then bogeyed the 13th and 15th holes, while Mickelson's 10-footer at the 13th gave him sole possession of the lead.