Phil Mickelson came from five strokes back to clinch his first Open title and fifth major on a dizzying final day at Muirfield.
The 43-year-old American triumphed by three shots from Sweden's Henrik Stenson, with English pair Ian Poulter and Lee Westwood four back, alongside Australia's Masters champion Adam Scott.
Mickelson surged to the third leg of a career Grand Slam of all four majors with a stunning five-under 66 to finish three under.
The left-hander, who won the Scottish Open last week, birdied four of the last six holes and was in tears on the final green as he hugged caddie Jim 'Bones' Mackay.
Former European Ryder Cup captain
BBC Sport at Muirfield
"What an unbelievable round by Mickelson. He almost
made it look simple. He played with such freedom. The
second shot he hit to 17 was absolutely majestic and
then he went on to birdie the last, which was the sign
of a true champion. He was the best guy out there this
"The only disappointment was Lee Westwood's round
today. He played a poor round and only he knows why.
It's not his last chance, but this one will hurt. Fortunately
he is extremely resilient and he will fight back."
The mercurial Mickelson's Open record had been modest up to now, despite a third place at Troon in 2004 and second at Royal St George's in 2011, as he slowly got to grips with a style of the game he initially "hated".
But a play-off victory over the Castle Stuart links in Inverness last week, and now his first Claret Jug, should make amends for his devastation at recording a record sixth runner-up spot in the US Open behind Justin Rose last month.
"This is such an accomplishment because I never knew whether I'd be able to develop my game to play links golf," said Mickelson.
"I played arguably the best round of my career, and shot the round of my life. It's such a difficult six-hole finish, I putted so good. It feels amazing."
He added: "The range of emotions I feel are as far apart as possible after losing the US Open. But you have to be resilient in this game. These last couple of weeks, these last couple of months, I've played some of the best golf of my career."
Mickelson, who won the Masters in 2004, 2006 and 2010 and the US PGA in 2005, continues the list of illustrious former champions at Muirfield, which includes such greats of the game as Gary Player, Jack Nicklaus, Lee Trevino, Tom Watson, Nick Faldo (twice) and Ernie Els, who was defending champion this week.
American Mickelson becomes the third consecutive player in his 40s to win the Open, after Els and Darren Clarke.
Mickelson delighted to "shoot the round of his life"
Westwood, seeking a first major title at the 62nd attempt, led by two going into the final day and moved serenely into a three-shot lead after five holes. But he took two to get out of a pot bunker on the short seventh and from then on was always struggling for momentum in a 75.
"I didn't play that badly, my round came unstuck at seven, eight and nine," said Westwood.
"Phil must have played really well. To birdie four out of the last six here on any day is good going. But to do it today on a breezy day with the flags blowing and in the Open Championship is exceptional."
Stenson carded 70 for his best finish in a major, while Ryder Cup hero Poulter surged from eight strokes back with a brilliant 67 on an overcast, breezy day in contrast to the heat and sunshine of the rest of the week in East Lothian.
Scott, who blew a four-shot lead to finish runner-up to Els last year, hit the front at one stage on a topsy-turvy afternoon that saw the lead change hands numerous times, but the 32-year-old faltered late on with a 72.
Tiger Woods began two behind Westwood and in prime position to strike for a 15th major title and first since 2008. But he went backwards from the first and ended with a 74 for two over.