Xander Schauffele edged clear of a heavily-congested leaderboard and will take a one-shot lead into the final round of the Charles Schwab Challenge.
Schauffele was part of a six-way logjam at the top until he rolled in his sixth birdie putt of the third day at Colonial Country Club to cap a 66 which earned him the outright lead on 13 under par.
The American overshadowed playing partner and world No 1 Rory McIlroy, who was just one behind after a birdie at the first before back-to-back mistakes at seven and eight left him with four strokes to make up, although he did produce a spirited back nine to salvage a 69 and get back to 10 under.
Justin Rose was tied for the lead until he bogeyed two of the last three holes, including a shocking miss from two feet at the 16th, while Schauffele's nearest challengers include three major champions in Jordan Spieth, Justin Thomas and Gary Woodland, with Branden Grace and Collin Morikawa completing the tie for second.
Overnight leader Harold Varner could not build on a birdie at the first and stuttered round in a level-par 70, two off the pace, while former Masters champion Patrick Reed vaulted into the mix with a superb 63 which gave him the clubhouse lead for many hours.
But it was Schauffele who would end the day in sole possession as he followed a quiet, outward 34 with a thrilling start to the back nine, almost holing out from the fairway at both the 10th and 11th holes and settling for kick-in birdies before he holed from 15 feet at the 15th to join Spieth at 13 under.
Schauffele blocked his tee shot to the short 16th and could not get up and down from the greenside rough, but he rolled in a confident 12-foot putt for a closing birdie at the last which put him in pole position to collect his fifth victory as a professional.
Thomas, Woodland and Grace had already signed for 66s which lifted them to 12 under with Morikawa (67) and Spieth, who was 13 under at the turn but struggled over the inward half, although he did well to limit the damage to a single dropped shot at the 15th as he signed for a 68.
Varner, still chasing his maiden win on the PGA Tour, made the ideal start when he birdied the first, but that would prove to be his lone gain of the round as he carded 16 pars and one bogey at 14 to keep him at 11 under alongside Daniel Berger.
McIlroy, Rose, Reed and Bryson DeChambeau are in a large group at 10 under, while Ian Poulter's 67 leaves him six strokes behind the leader heading into the final 18 holes.
McIlroy's day started brightly as a birdie at the first took him to four under for the week on the opening hole, but poor tee shots - with irons - at seven and eight led to a pair of dropped shots, but a good up-and-down from the sand at 11 clawed one back and a 25-footer for birdie at 14 got him back into double-digits under par.
The world No 1 did miss further good chances at 15 and 17, while 2018 champion Rose got himself into contention with five birdies on the front nine alone, although he also double-bogeyed the fifth after an ambitious second from the rough proved costly, and a sixth birdie of the day propelled him to 12 under.
But Rose's focus deserted him on his short par putt on the 16th green, and he bunkered his approach to the last and two-putter from 12 feet for bogey to slip back to 10 under par for the tournament.