Louis Oosthuizen had never been to the TPC Boston until his week, although he knew what to expect in the Deutsche Bank Championship.

This is a course that tends to favor power, and the South African has plenty of that. It's also a course where players make a lot of birdies, and no one has made more than his 19 over the opening three rounds.

"If you're playing well, you can shoot really low numbers," Oosthuizen said.

Oosthuizen carried out the scouting report to near perfection Sunday in the third round, at least for a two-hour stretch that was close to flawless. He made eight birdies in a nine-hole stretch — the exception was No. 3, where he missed a 5-foot birdie putt — before he cooled down on the back nine and had to settle for an 8-under 63.

It was enough to build a three-shot lead over Rory McIlroy, who was exceptional on the back nine to post a 67 that kept the tournament from getting away from him.

Tiger Woods and Dustin Johnson were still in the mix, just barely. Woods made back-to-back birdies late in his round for a 68, while Johnson's Ryder Cup hopes took a strong turn in the right direction with a 65.

Oosthuizen set a trio of tournament records on another sun-filled day south of Boston, until some dark clouds and a light rain showed up in the final hour. He made seven straight birdies. He shot a 29 on the front nine. And he completed 54 holes in 19-under 194.

But the Labor Day conclusion was sure to include a lot more work ahead for Oosthuizen.

Yes, the TPC Boston allows for birdies, though not just for him. McIlroy and Johnson also have 19 birdies going into the final round. And while Woods has never come from further than five shots behind to win on the PGA Tour, six years ago in Boston he rallied from three back with a 63 that toppled Vijay Singh by two shots.

To see Oosthuizen threaten to run away from the field was not discouraging as much as it indicated what was out there. Earlier on Sunday, Keegan Bradley had a 63 despite a bogey on the 17th and failing to make birdie on the par-5 18th.

"With the conditions like this, we're going to have to shoot some good numbers," Woods said. "It's definitely gettable. Louis played a good round, Keegan played a good round early. You can post 4, 5, 6 under par on that front nine if you get it going early. The back nine is certainly gettable, as well. I think I shot 30 on the front nine against Vijay. I'm going to need a quick start like I had that day.

"That's basically what Louis did and that's what Keegan did, as well," he said. "You get off to quick starts, you can get it going."

Oosthuizen had some help with a pure putting stroke that matched his sweet, simple swing, which has become the envy of the PGA Tour. His birdie streak began with a chip from behind the short par-4 fourth hole to 6 feet. He had a simple up-and-down from next to the green on the par-5 seventh. And it ended with a shot into 2 feet on No. 10. Along the way, he holed birdie putts of 20 feet on Nos. 5 and 6, a 40-footer on the par-3 eighth and a 25-foot birdie putt on the ninth.

"After making the putt on 8, I felt like I can't miss anything," Oosthuizen said. "And then on 9, you just needed to get it high enough out, and then it's all about the speed, and I got it perfect again. ... You know, standing on the putt on 11, I thought I had a perfect line again. The last thing I thought was missing it."

Alas, he missed it, though not by much.

It was at that point in the round McIlroy came back to life. He started the third round with a one-shot lead, played reasonably well for 10 holes and was six behind. Then, Boy Wonder had to watch the South African hit a tee shot on 11 that covered the flag, just a little strong to 20 feet beyond the hole. McIlroy went after his shot, high with a gentle draw that dropped next to the hole and settled 6 feet behind the flag.

He rolled it in for a birdie, then stood at the back of the green waiting for Oosthuizen to clean up his par.

McIlroy held out his arm and clenched his fist and said to Oosthuizen proudly, "I've got honors."

They laughed, exchanged a high-five and walked toward the 12th tee, and McIlroy said with a grin, "I feel like I've got a chance."

Rivalries in golf, at least in the last 50 years, seem to be more interesting when the players are a generation apart. Coming from the same generation, this is a good place to start. McIlroy already has two majors, both by eight shots. Oosthuizen, who never looks like he's going to hit a bad shot, won his sole major by seven shots at St. Andrews in the 2010 British Open.

McIlroy kept up the pace with a tee shot on No. 12 that glided high and far, the longest of the day at 326 yards, setting up a wedge to 5 feet.

"The birdie on 11 sort of sparked things, and I hit a couple of great shots into 12," McIlroy said. "If you're talking about momentum in a round, I think 11 definitely gave me some momentum."

Oosthuizen thought briefly about a 59 — remember, he once had a 57 on his home course at Mossel Bay along the Garden Route of South Africa — and had to settle for a 63. He had a six-shot lead on the 10th hole and it was down to only three at the end of the day.

If McIlroy winds up with the trophy Monday, he may well have won it on Sunday afternoon.

"Rory just kept on coming at me, and I knew that," Oosthuizen said. "I knew I needed to make birdies to keep a five- or six-shot lead. So a bit disappointed in that I had a lot of opportunities on the back nine for birdies, and I only made two with a bogey on 17. All in all, started the day one behind, going into tomorrow leading by three. I'm very happy."