Thomas tied for lead as Spieth and Johnson lurk at TPC Boston
Major winner Justin Thomas was flawless as he moved into a tie for a one-stroke lead with Marc Leishman after the third round of the Dell Technologies Championship.
Reigning US PGA Championship holder Thomas shot a bogey-free eight-under-par 63 at the second FedEx Cup play-off event on Sunday.
Thomas ended his third round with eight birdies to be 12 under through 54 holes at TPC Boston. The American also set a FedEx Cup play-off record by finishing with 12 threes on his scorecard.
Full of confidence after breaking through for his maiden major at Quail Hollow, Thomas did not drop a shot, gaining strokes at the first, fourth, sixth, ninth, 10th, 12th, 14th and 17th holes as he improved 14 positions.
Leishman caught fire with his putter on the back nine, which led to three successive birdies from holes 13 through 15.
The Australian quietly began the week 20th in the FedEx Cup standings, but he could move up considerably with a strong round on Monday.
Paul Casey, who is riding a streak of four consecutives top-five finishes in play-off events, will head into the final round one shot back at 11 under after his 67.
Former world number one and three-time major champion Jordan Spieth is two shots off the pace heading into the deciding round.
Spieth worked his way back into contention with a third-round 66, joining Grayson Murray (67) and Adam Hadwin (68) at 10 under.
World number one Dustin Johnson is a stroke further back after birdieing four out of his last five holes during a bogey-free 66.
Johnson claimed the first play-off event via the Northern Trust as he eyes back-to-back titles.
Second-round leader Jon Rahm (71) is also nine under after a disappointing penultimate day that was at least capped with a birdie on the par-five 18th hole.
Meanwhile, Masters champion Sergio Garcia slammed and broke his putter after leaving an eagle putt woefully short on the fourth hole, but on his next shot, he sunk a 14-foot putt with his three-wood.
There was only so much magic in the three-wood, however. Garcia's third-round rapidly went south, as he bogeyed four of his next five holes to be two over the card.