England's Paul Casey fired a second straight 66 at the Deutsche Bank Championship to put himself a shot behind leader Kevin Chappell at the halfway point in Massachusetts.
Casey, after starting at the 10th, posted four of his five birdies over his final seven holes of the day in a flawless second round, and was tied for second alongside Jimmy Walker in the second of four season-ending FedEx Cup play-off events.
Chappell was six under through eight holes of his second round - an eagle at the par-five seventh the highlight - and went on to sign for a 64, with a bogey at the par-four 13th the only blot on his copybook.
"It was a good day's work. If you'd told me that at the beginning of the day, I definitely would have taken it," Chappell said on www.pgatour.com after moving to 11 under par for the tournament.
"I feel like I've learned a lot this year in being in contention and handling myself well, and I look forward to applying that this weekend."
Walker, like fellow American Chappell, carded a sparkling 64 which included an eagle on seven.
Brian Harman sat two shots off the pace on nine under after posting a 65 on Saturday, with world number two Dustin Johnson (66) and Smylie Kaufman (66) a further stroke back and tied for fifth.
Englishman Justin Rose (67) was among a cluster of players on seven under, alongside first-round co-leader Ryan Moore (70), Patrick Reed (67), Brian Stuard (69), Daniel Berger (68) and Gary Woodland (66).
Rose got himself firmly in the mix thanks largely to a spell of three birdies in four holes from the first, having started at the 10th, in his bogey-free round.
Northern Ireland's Rory McIlroy registered a 67 in an up-and-down round which featured seven birdies and three bogeys.
Open champion Henrik Stenson slipped to joint 30th after a one-under-par 70, the Swede's cause hindered by a double-bogey at the par-four first - his 10th hole of the day - and then bogeys on four and five.
Luke Donald (71) and world number one Jason Day (71) just made the cut on one under - tied in 62nd place among a group of 11 players - with Scotland's Russell Knox (67) also safely into Sunday on two under.
Scotland's Martin Laird carded a much-improved 68 but it was not enough to see him into the final two rounds after his opening 75. He missed the cut along with Northern Ireland's Graeme McDowell, who followed up his first-round 74 with a 70.
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