NORTON, Massachusetts, Sept 3, 2012 (AFP) - McIlroy, of Northern Ireland, finished at 20-under-par 264 for his third victory of the season. He now has five career PGA Tour wins.
"I didn't finish off the way I would have liked," McIlroy said. "But I got there in the end. I'm very happy."
Oosthuizen closed with an even-par 71 on the TPC Boston to finish solo in second at 19-under at the $8 million tournament. The 2010 British Open champion lost earlier this year to Bubba Watson in a playoff at the Masters.
Tiger Woods parred eight consecutive holes beginning at the 10th and then made birdie on 18 for a final round five-under 66. Woods finished third at 18-under-par 266.
Woods also surpassed the $100 million mark in PGA Tour earnings with his third-place finish.
Dustin Johnson (70) and Phil Mickelson (66) tied for fourth at minus-14 in the Monday finish. It marked Mickelson's best finish since the Masters, where he placed in a tie for third.
The 23-year-old McIlroy, who won the PGA Championship last month, vaults into the top spot in the FedEx Cup standings.
He joined Woods as the only three-time winners on the PGA Tour this season but he had to overcome a couple of mistakes on the final holes to do it.
With a half dozen holes to play, McIlroy had a three-stroke lead. He began to stumble a bit down the stretch before recovering with a key bogey on the 17th hole.
"That was more survival the last few holes," said McIlroy, who earned $1.4 million in prize money for the win. "It's my third victory of the year and it's great to get a victory in these playoffs."
Oosthuizen, of Mossel Bay, missed a 12-foot birdie putt on the 18th hole that would have got him into a playoff.
"I started off a bit shaky, but I played really well (down the stretch)," said Oosthuizen, who battled through the pain of a chest injury. "I might just take a rest until Thursday."
Woods began his round by making an early charge with four birdies on the front nine and then finished with a nice birdie on No. 18.
Charley Hoffman parred the final hole and managed to slip into the top 70 in the FedEx Cup race which qualified him for the third playoff event next week in Indianapolis.
Johnson is hoping his 70 will help him get selected to the US Ryder Cup team. Brandt Snedeker shot a closing 67, which will help him in his bid to make the team.
Team USA captain Davis Love will announce his Ryder Cup picks Tuesday in New York.
Leading final-round scores here on Monday from the $8 million Deutsche Bank Championship (USA unless noted, par-71):
264 - Rory McIlroy (NIR) 65-65-67-67
265 - Louis Oosthuizen (RSA) 66-65-63-71
266 - Tiger Woods 64-68-68-66
270 - Dustin Johnson 67-68-65-70, Phil Mickelson 68-68-68-66
271 - Brandt Snedeker 69-70-65-67
272 - Jeff Overton 64-71-69-68, Adam Scott (AUS) 69-69-68-66
273 - Bryce Molder 65-69-68-71
274 - Ryan Moore 64-68-70-72, Kevin Stadler 68-71-69-66
275 - John Senden (AUS) 66-69-70-70
276 - Keegan Bradley 71-73-63-69, Jim Furyk 69-72-65-70, Seung-yul Noh (KOR) 62-71-75-68, Steve Stricker 69-69-68-70, Lee Westwood (ENG) 68-71-69-68
277 - Jason Dufner 67-66-70-74, Webb Simpson 69-70-66-72
278 - Jonas Blixt (SWE) 67-72-71-68, Troy Matteson 72-67-70-69, John Merrick 68-72-68-70, D.A. Points 68-65-71-74, Dicky Pride 69-72-69-68, Nick Watney 72-69-66-71