A brilliant birdie-birdie finish from Phil Mickelson saw the American win his first Open Championship and a fifth career major.
Five weeks after finishing runner-up at the US Open for the sixth time when his hopes were dashed by Justin Rose, he gained revenge at the expense of another Englishman Lee Westwood, who had begun the day with a two-shot lead.
His round of 66 at Muirfield equalled the tournament's best of the week and could not have been more perfectly timed.
He won by three shots from Sweden's Henrik Stenson, who carded a round of 70.
The 43-year-old Mickelson, who a week ago won his first title in Britain with victory in the Scottish Open, teed off two over - five off the lead - but steadily came through the field and superb approaches to the last two holes clinched the title.
Mickelson took advantage of the fluctuating final-round fortunes of Westwood, Masters champion Scott and world number one Tiger Woods.
Westwood allowed a three-stroke lead to slip through his fingers and Scott must have felt history was repeating itself as, just like 12 months ago at Royal Lytham when he squandered four shots in the last four holes, he led on the back nine but had a quartet of successive bogeys from the 13th.
And just when Woods - still trying to add to his tally of 14 majors after a five-year drought - looked like making a late charge after a birdie at the 14th to get back to one over, he bogeyed the next hole to drop out of the running.
Poulter had given himself a real chance with a four-under 67, including a run of eagle-birdie-birdie-birdie from the ninth, but his one-over clubhouse total was eclipsed in magnificent fashion by Mickelson.
"What a fun day. This is some of the best golf I have ever played," said Mickelson.
"It's the best I've ever putted, they kept flying into the hole and every iron shot was right on line.
"You can't make it happen, you have to let it happen and I hit good shots which had good bounces giving me good putts that I made."
The American added on Radio 5 Live: "Playing this championship was the biggest challenge of my career and I didn't know if I had the skills to win on links golf but I played some of the best links golf I have ever played.
"It is amazing to be part of any Open Championship and to win at Muirfield feels amazing.
"I have such an incredible difference of emotions from where I was a month ago with such a heart-breaking loss at the US Open.
"This is probably the greatest and most difficult win of my career."
Westwood, who finished with a round of 75, admitted things began to go wrong for him just as he had got himself into a three-shot lead but gave full credit to Mickelson's performance.
"My round came unstuck a bit at seven, eight and nine," he told the BBC.
"Phil must've played really well, five under par was a good round of golf this afternoon.
"If you birdie four of the last six anywhere that is good going."
Darren Clarke finshed as the best Irish performer on seven over in a tie for 22nd after a 72.
Offaly's Shane Lowry produced his best round of the week to shoot 70 and finish on nine over with Padraig Harrington two shots further back while Graeme McDowell shot a 77 to finish on 12 over par.