Brooks Koepka had his rivals on the ropes but could not deliver a knockout punch and had his lead whittled to two strokes over Adam Scott after the third round at the PGA Championship on Saturday.
The quiet American looked set to match the largest 54-hole lead in tournament history when he bolted five shots clear after 13 holes from a large group including Tiger Woods at Bellerive.
But a couple of loose swings led to consecutive bogeys and suddenly it was game on, a four-under-par 66 not exactly what Koepka had in mind a couple of hours earlier at Bellerive.
A 12-under 198 total still left Koepka within sight of his third major title in 14 months, but the two-time US Open champion's grip on the Wanamaker Trophy had loosened.
Australian Scott produced a ball-striking round of impeccable quality, a 65 the best score of the afternoon, marred only by a couple of missed putts, including a seven-footer at the last.
A former world number one and the 2013 Masters winner, Scott muscled his way into second place on 10-under, while Spaniard Jon Rahm (66) and Americans Rickie Fowler (69) and Gary Woodland (71) were three behind.
Tiger Woods, whose earlier charge on the easier front nine raised the massive gallery's excitement to fever-pitch, was among a logjam of six trailing by four shots.
He parred every hole on the back nine and his 66 matched his lowest round in a major this year, but he was a little disappointed, not least with a three-putt at the par-five 17th.
"It could have been a little bit closer but I've got a shot going into tomorrow," he said.
Earlier, Koepka brought Bellerive to its proverbial knees with five birdies in an outward half of 30 strokes. And he made it look ever so easy, bludgeoning his drives massive distances and honing in on the pins with unerring accuracy.
He holed only one lengthy putt, the other four birdies coming from tap-in range, or close to it. Koepka seemed an unlikely candidate to falter, but falter he did.
A bogey at the 14th, where he found a greenside bunker, ended a run of 43 holes without a dropped shot, and he promptly bogeyed the next too after his drive ended behind a tree, from where he took a penalty drop. Those errors brought Woods back into contention.
Ten years removed from his 14th and most recent major title, he displayed shades of his pre-back surgery greatness with a near-flawless front nine on the rain-soaked layout.
Taking advantage of the marshmallow-soft greens, he hit a series of precise approach shots and converted with the putter to plunder five birdies.
Only a three-putt bogey at the fifth hole halted his progress, though he put the setback quickly behind him to birdie the next three holes.
Woods was among 77 players who returned early on Saturday to complete the weather-delayed second round. Woodland was not among them, having finished his round on Friday morning.
His 10-under-par 130 score matched the lowest halfway total in major championship history, and he enjoyed a one-shot halfway lead over Kevin Kisner, and a two-shot cushion over Koepka.