Watney knocked in a 40-foot birdie putt from the fringe on the par-3 16th, then completed his five-shot rally with a two-putt birdie on the 18th hole. He closed with a 4-under 68 for his second career victory, earning a trip to the Masters.
Rollins let this one get away.
He had a three-shot lead with five holes to play until making a bogey with a poor chip on the 14th, another bogey from a plugged lie in the bunker on the 16th, and failing to hit the green on the par-5 18th, leading to a par. He shot a 74.
Watney finished at 11-under 277 ' the same total Ryuji Imada had last year when he was runner-up by eight shots to Tiger Woods, who has not played since knee surgery after winning the U.S. Open last June at Torrey Pines.
Lucas Glover and Camilo Villegas also had their chances.
Glover briefly was within one shot of the lead and was still in the mix until he pulled his tee shot on the 17th into rough so thick that he had to hit out short of the green and missed a 7-foot par putt. He birdied the last hole for a 68 and tied for third, two shots behind.
Villegas was within one shot until a three-putt from 10 feet on the par-5 sixth, and Rollins collapse offered the Colombian another chance. But he hit out of the rough and over the green at the 17th to make a bogey, and his 40-foot eagle putt on the 18th hole stopped a few inches above the hole. He closed with a 72.
Watney was five shots behind going into the final round and was an afterthought most of the day, never getting closer than two shots until the tournament swung in his favor on the 16th.
Rollins tee shot found the left bunker, and the ball resembled a fried egg. The lie was so severe that the best he could do was blast out across the green and into the rough, 25 feet away. He chipped to 2 feet for a bogey. Watney was 40 feet away on the fringe, facing a putt that broke sharply to the left. But the pace was perfect, the ball caught the left edge and dropped, and Watney widened his eyes and pumped his fist.
That gave him a tie for the lead, and after they exchanged pars on the 17th, he came up with the shot that mattered on the 18th, finding the top shelf of the green and coaxing his long eagle putt a few feet away.
Rollins 12-foot birdie putt that would have forced a playoff didnt have a chance.
Matt Jones of Australia matched the low round of the week on the South Course with a 64 and finished alone in fifth.
British Open and PGA champion Padraig Harrington broke 70 for the first time all week in his PGA Tour debut this season and tied for 24th at 1-under 287. Phil Mickelson went the other direction, posting progressively higher scores each day until closing with a 75 on Sunday to tie for 42nd. He finished at 290, his highest 72-hole score ever in the Buick Invitational.
Rollins never lost the lead until the final hole, although he tried.
He started the final round the way he ended the third round, with a three-putt bogey on a putt that caught the lip. He dropped another shot on the second hole when he went after the flag in the back right of the green, the ball catching a torrey pine on its way down. Rollins chipped too hard to 10 feet and missed another putt.
Rollins had to save par from 5 feet on No. 4, which settled him, and then it was Villegas who came unglued.
Villegas made a 12-foot birdie to get within one of the lead as he headed to the par-5 sixth, the easiest hole on the South Course. He came up short of the green, hit a decent flop shot to 10 feet, narrowly missed the birdie putt, then missed again from 3 feet for par.
He tugged at his painters cap after a two-shot swing when Rollins converted a simple up-and-down. On the next hole, Villegas drove into the right rough and tried to hit a huge slice around the trees, but wound up near the eighth tee and couldnt chip onto the green. He had to get up-and-down to escape with bogey, falling four shots behind.
Rollins holed a 20-foot eagle on the 13th that restored his lead to three shots, and he was poised to capture his third PGA Tour victory until a couple of misses and some timely birdies by Watney.