NORTON, Mass. (AP) -- PGA champion Justin Thomas ran off eight birdies on a long, wet TPC Boston for a tournament-best 63, giving him a share of the lead with Marc Leishman going into a Labor Day finish in the Dell Technologies filled with the game's best players.
The FedEx Cup playoff event in Boston has a history of delivering big moments, and this was set up for another.
Leishman, who won at Bay Hill this year, also played bogey-free for a 65 on Sunday to join Thomas at 12-under 201.
Eight players were separated by three shots going into the final round, a listed that included Jordan Spieth and Dustin Johnson, Paul Casey and Jon Rahm. Still very much in the mix was Phil Mickelson, only four shots behind.
"There is a heightened something to these playoff events that bring out certain champions for the most part," Spieth said Sunday after finishing with two straight birdies to nudge closer to the lead, just two shots behind. "It's going to be a throw-down tomorrow."
Thomas had his third round this season at 63 or better - a list that includes his 59 at the Sony Open and a 63 at the U.S. Open - to turn a five-shot deficit into a share of the lead and a chance to win for the fifth time this year.
He birdied six of the first 10 holes, the longest at about 12 feet. He played down the 13th fairway on the redesigned 12th hole for the third time this week and holed a 50-foot birdie putt, and then added a pair of 25-foot birdie putts.
And he didn't even birdie any of the par 5s.
"I just felt I had total control of my game," Thomas said. "But it's crazy to think I did that and parred all the par 5s. That's a little bit of a bummer, if I could somehow have a downside to the day. But like I said, I'm extremely pleased and put myself in a great position to win the tournament."
And he has plenty of company.
Casey played in the final group at the TPC Boston last year, but Rory McIlroy ran him down with a 65 to overcome a six-shot deficit. Casey also played the three par 5s without a birdie, missing a 12-footer on the final hole that would have given him a share of the lead.
Then again, the TPC Boston played longer than ever with heavy air and a light rain that never left Sunday. Thomas was stunned when he smashed a driver on the 18th and couldn't carry a bunker complex only 260 yards out. He normally flies a tee shot like that 300 yards.
The forecast for Monday was mostly sunshine, and if the course remains softer from rain, this could be a typical shootout. Leishman figured the winning score would be in the 15- or 16-under range.
"That would be my plan, to just try and do what I've been doing - give myself as many chances as I can and try and make them," he said.
Rahm had a two-shot lead and still had the lead until running into trouble on the back nine, making three bogeys until he ended his round with a birdie for a 71. .
"I will be a little bit frustrated for a while because it always is bad when you're making good swings and things don't happen," Rahm said. "I'll probably get to the hotel, lay down for a little bit and realize the fact that I'm still three shots back."
Most frustrating was that everyone around him was making a move.
It was especially critical for Johnson, who played the third round with Thomas and couldn't buy a putt. Johnson, coming off a playoff victory last week in New York, sarcastically pumped his fist when he made a birdie on No. 14, and then he kept right on going. The only hole he didn't birdie coming in was at No. 17, where he missed a birdie chance for 10 feet.
"I just wanted to get myself in position to be in range of the leaders," Johnson said.
He was three behind Spieth going into the final round of The Northern Trust and ended up winning in a sudden-death playoff.
PGA Tour rookie Grayson Murray (67) and Adam Hadwin (68) were at 10-under 203 along with Spieth, who has made only two bogeys over his last 45 holes. Spieth shot a second straight 66 and was surprised that left him two shots behind, all because of Thomas and Leishman.
"I couldn't have shot a whole lot better," Spieth said. "I thought four back starting the day, if I could cut that in half, then that would be a tremendous goal. So goal achieved, maybe."
Mickelson dropped a shot on the par-5 seventh with a wild tee shot and missed a 4-foot birdie putt on the ninth hole, but otherwise kept in the game. This is the first time Mickelson has opened with three straight rounds in the 60s since the St. Jude Classic in June, which also was his last top-10 finish.
Monday could go a long way in persuading U.S. captain Steve Stricker to pick him for the Presidents Cup. Still to be decided is the final 10 who automatically make the team. Kevin Chappell shot a 69 and moved into position to overtake Charley Hoffman for the 10th spot.