The pain went away on the back, which the South African attributed to an adrenaline rush.
McIlroy and Oosthuizen turned it into a two-man race, with Woods lurking until he couldn't convert enough putts. In the end, neither could Oosthuizen. He missed from just inside 10 feet for par on the 17th and from 12 feet on the 18th.
"I probably made all my putts yesterday," Oosthuizen said.
There was other drama at the Deutsche Bank Championship, though it was not nearly as compelling as the top of the leaderboard.
Charley Hoffman went from the first page of the leaderboard to an unimaginable collapse until he steadied himself at the end. Hoffman, who was 13 under after a birdie on the eighth hole, played his next nine holes in 8-over par, including a quadruple-bogey 7 on the par-3 11th. He came to the 18th needing a par to finish among the top 70 in the FedEx Cup and advance to the third playoff event next week in Indianapolis.
He went over the green in two, barely chipped onto the putting surface, and then ran his putt 12 feet by the hole. He made the putt for par, and moves on.
"I didn't expect to be playing next week," Hoffman said. "Shooting 42 on the back nine, I don't think I deserved to play next week. But I guess I've got another chance."
Others who advanced included Dicky Pride, who birdied his last two holes to get the 70th spot by one stroke over Jonas Blixt; and Chris Kirk, who stumbled at the start only to birdie four of his last five holes.
Oosthuizen had a three-shot lead at the start of the final round, though he was never expecting an easy time. McIlroy rallied to cut a six-shot deficit in half on the back nine of the third round to give himself a chance, another example why he is No. 1 in the world.
Sure enough, McIlroy came out firing with three straight birdies, starting with a two-putt from the fringe on the par-5 second.
The fifth hole changed everything.
Oosthuizen reached for his shoulder after a horrific snap hook off the tee. The ball dove into the woods and landed in the middle of shoulder-high bushes, leaving him no option but to take a penalty drop out of the hazard. He laid up short of the creek and two-putted for double bogey. They were tied, because McIlroy's tee shot found a clump of native grass on the edge of a bunker, and he had to chip out short of the creek and made bogey.
Oosthuizen, though, was clearly hurting. He couldn't get through his swing on the next tee shot, which sailed into the bunker and kept him from attacking the pin. That's what McIlroy did, hitting 9-iron into 3 feet for birdie and his first lead. He never gave it back.
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