AUGUSTA, Ga. - As he came off the 18th green, Phil Mickelson knew he couldn’t win the Masters. He was surely thinking he could have shot 64, perhaps even 63 if only he’d avoided Rae’s Creek on the 12th hole.

If not for yanking a 9-iron with what he called “a terrible swing,’’ Mickelson could well have earned his third green jacket, the most treasured prize in golf, with what could have been an historic final round.

Indeed, it’s rare when you can say that someone who shot 67 on Masters Sunday gave the tournament away, but how could anyone watching come away from this day thinking anything else?

Mickelson was dazzling early, shooting 30 on the front nine to put himself within one shot of the lead. And as it turned out, Kenny Perry’s collapse on the final two holes that allowed Angel Cabrera to win in a playoff was all the more reason to believe it could have been Mickelson’s day.

Yet somewhat strangely, golf’s most famous lefthander appeared more exhilarated by his near-miss than devastated. He shook hands with well-wishers, smiled his sheepish smile, and ran the gauntlet of media interviews.

Under questioning Mickelson didn’t address his mood directly, but and it seemed that any disappointment was tempered by the way he prevailed in his individual duel with one Tiger Woods.

He’d shot 67 to Tiger’s 68 in a pairing that turned out to be more meaningful than expected, but only Mickelson truly had a chance to win the tournament. For someone who has had to fight the perception that he can’t beat Tiger in a staredown, it might be quite significant.

“It was fun,’’ he said when asked about their pairing. “We’ve had some good matches in the past, but I’m usually on the wrong end of it. This was fun playing with him.’’

Slideshow   Look back at the 2009 Masters Round-by-round pictorial review of this year's tournament at Augusta. more photos

Actually, you can make the case that Mickelson missed a golden opportunity to eat Tiger’s lunch and win the Masters with him alongside, the way he did to Mickelson in 2001, the only other time they’d been paired on a Masters Sunday.

Yet maybe this was a start toward Mickelson standing up to Tiger and putting some real teeth in their rivalry. It was the first time he’s had a real chance to win a major since his collapse at Winged Foot U.S. Open in 2006, so maybe he’s exorcised some demons that will allow him to beat Tiger when it counts most.

You never know with Mickelson. The thrill of watching him is that you never know what he’ll do next. He always seems as capable of foolish mistakes as the brilliance he displayed on Sunday.

For that matter, we’ll never know for sure whether the double-bogey on No. 12 was merely the result of a bad swing, as Mickelson said, or another example of him getting too bold and trying to hit the perfect shot in a situation that begged for caution.

This wasn’t anything like his “I-am-such-an-idiot’’ moment at Winged Foot in 2006, when he blew the U.S. Open at least partly because he tried to pull off an impossible recovery shot on the 18th hole. But it was something of an unforced error that Mickelson surely will remember for a long time.

Not only did it result in a double-bogey at a time when he was only one stroke out of the lead, but it killed his mojo, as his hot putting stroke deserted him the rest of the way, leaving him three shots short of a playoff.

Until then Mickelson was starting to look like the best bet on the board after he tied the Masters record with his 30 on the front side, and produced some of the loudest roars echoing through the Georgia pines that anyone could remember.

With the back nine full of birdie and eagle opportunities, Mickelson admitted afterward he was thinking that “I could get to 13- or 14-under par.’’

Final round scorecards at the 2009 Masters: Woods and Mickelson Hole 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Total Par 4 5 4 3 4 3 4 5 4 4 4 3 5 4 5 3 4 4 72 Phil Mickelson 4 4 3 3 3 2 3 4 4 4 4 5 4 4 4 3 4 5 67 Tiger Woods 4 4 4 3 4 3 4 3 4 4 4 3 4 4 4 2 5 5 68

He had to get past No. 12 to even think about it. The 12th is part of Masters lore, of course, because it can play so devilishly when the wind is swirling at Amen Corner. It played over-par on Sunday, ranking as the second-toughest hole on the course, but the wind wasn’t causing problems late in the day.