Australian Adam Scott fired an eight-under par 63 for a share of the lead at the halfway stage of the Deutsche Bank Championship in Boston.
Scott shot the lowest round of the day and is on 10 under alongside Masters champion Charl Schwartzel of South Africa and American Bubba Watson.
Schwartzel birdied six of seven holes after making the turn for a 66 while Watson managed a 64.
Brandt Snedeker is a shot back thanks to a hole-in-one at the par-three 16th.
World number one Luke Donald is on six under after dropping two shots over his last three holes.
The event is the second leg of the season-ending US PGA Tour play-offs which offer a $10m (£6.12m) top prize.
"This was a really solid round," Scott said. "I turned it around with the putter after yesterday and I'm happy to be back in the mix again."
Scott, who won last month's World Golf Championships event at Akron, had six birdies and an eagle and although he missed a 25-foot birdie putt at his final hole - the ninth - which would have given him the outright lead, the Australian was still pleased with his performance.
"This one is right up there," he said. "Hopefully the weather holds up and we have another good one tomorrow."
Schwartzel, who also started at the 10th, bogeyed the 11th before a birdie at the 16th. After a bogey at the 18th, he then birdied four holes in a row to challenge.
Watson managed six birdies, a bogey and, for the second day, an eagle on the par-five seventh.
There was also a hole-in-one at the 16th for Australian Greg Chalmers in a round of 65 that left him on five under.