Oberholser was within one shot of Mickelson most of the back nine, but he needed an eagle on the final hole to force a playoff, then missed a 10-foot birdie putt when the tournament was sealed. He moved up to No. 29 in the playoff standings; had he made the birdie putt, he would have gone to No. 20 and clinched a spot at East Lake for the Tour Championship.
John Mallinger and Bo Van Pelt moved into the top 70 to advance to the third round next week in Chicago.
Woods and Mickelson played together for the third time this week, but the final round put an end to the chatter, and seemed to double the size of the gallery that had followed them around the first two days of the tournament.
Woods twice was in position to apply some pressure on Lefty and both times failed, a sign of things to come. Woods had a 15-foot eagle putt on the par-5 second hole that he left short, and a 65-foot eagle putt on the 298-yard fourth hole that he three-putted for par.
Mickelson, who matched Woods' birdie at No. 2 with a nifty pitch, hit his bunker shot on No. 4 just onto the fringe about 15 feet away and made that for birdie. Mickelson stretched his margin over Woods to three shot with an approach on No. 5 into about 4 feet.
Woods had another advantage on the par-5 seventh, his third putt for eagle on the front nine. He two-putted for birdie, but Mickelson matched him again with a long bunker shot to 6 feet.
The difference in their games was largely on the greens. Mickelson took only 11 putts on the front nine, including a 12-foot par save on the sixth when he flew the green. Woods had 17 putts, the longest he made was 4 feet for par on the third hole.
Woods fell five shots behind at the turn, and even when Mickelson gave him a slight opening, the world's No. 1 player stumbled trying to bust through the door.
Despite holding a three-shot lead over Oberholser - and still five over Woods - Mickelson went at the flag on No. 12 and came up short into the hazard. Mickelson chipped up to 5 feet and missed to make double bogey. Woods had a prime chance to make it a three-shot swing, but his 15-foot birdie was well off line.
And this came one hole after Woods missed an 8-foot birdie, as Lefty made from 6 feet for par.
Woods tried to keep it interesting with a 40-foot birdie on the 14th hole to get within two shots, but that was as close as Mickelson allowed him to get. The key shot came on the par-3 16th, after Woods hit 8-iron into 10 feet. Mickelson followed with an 8-iron that never left the flag and stopped 6 feet below the hole.