With others at the top of the leaderboard, most notably world number one Tiger Woods, struggling the 40-year-old Englishman, playing in the final pairing, seemed perfectly placed to finally realise his boyhood dream.
Just as it had on numerous other occasions in his 61 previous bids to win one of golf's four crown jewels, hope was devoured by bunkers, tangled rough and the brilliance of others.
Westwood is used to answering questions about his ability to close out majors and shrugged off his latest setback, although this one will surely hurt more than most.
"I'm not too disappointed. I don't really get disappointed with golf any more," said the third-round leader who ended up joint third after a four-over 75.
"I'll keep putting myself in contention. I didn't do a lot wrong today. I just didn't do enough right," he told reporters.
Westwood glanced at the scoreboard on the seventh to see that he was alone on three-under, the only player left in the tournament below par after four days on a brutish links course.
He took an age to size up his tee shot at the 184-yard par-three that was playing into the wind.
Finally he settled over his ball and hit what looked to be the perfect shot, launched directly towards the pin.
Sadly his ball stalled before the green and landed in one of the deep crater-like bunkers that litter the course.
Westwood had seemed calm and collected until then, refusing to panic when he bungled the third hole and hitting back with a birdie at the fifth to roars from the expectant galleries.
However, as his ball plugged in the sand in front of a sheer face, he turned around and snapped at a photographer who he said had clicked his shutter at the top of his backswing.
Suddenly former world number one Westwood looked vulnerable.
Faced with a horrible bunker shot, his first attempt saw his ball roll back into the sand. His second was better and he courageously holed a sizeable bogey putt to limit the damage.
His ball was sucked into sand again at the eighth, resulting in another dropped shot.
The round was fraying and it began to unravel at the ninth when he found the rough, then a bunker and walked off with only a par from a hole playing partner Hunter Mahan eagled after a magnificent second shot.
Seemingly in the blink of an eye his lead had gone but, unlike Saturday when he also surrendered a three-stroke advantage before forging ahead to start the fourth round with a two-stroke lead, there was to be no grandstand finish.
After a missed birdie putt at the 10th, Westwood glanced over his shoulder to see Australian Adam Scott had moved into the lead.
The shouts of 'C'mon Lee' from the crowd took on a forlorn tone and when the Englishman bogeyed two par-threes on the back nine, his intended victory march had begun to resemble a wake.
Phil Mickelson was rightly lauded for a breathtaking final round of 66, snatching the title by three shots, but Westwood will again face sniping about his failure to seize his big chance.
A subdued Westwood, veteran of eight Ryder Cups and with 22 European Tour titles to his name, took some consolation from 43-year-old Mickelson's perseverance.
"They should rename this the over-40s championship because it seems you have to be 42 or 43 to win it these days," he said through gritted teeth referring to last year's victory by Ernie Els and the 2011 triumph of his close friend Darren Clarke.
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