Camilo Villegas held a one-shot lead going into the final round of the BMW Championship in St Louis.
The Colombian could not finish his third round on Saturday with him tied with Jim Furyk on 12-under-par.
But he returned on Sunday and sunk a birdie putt on the penultimate hole of his round to move into pole position to win his first PGA Tour event.
Furyk and Anthony Kim, who ended on nine-under, are the leading names in the chasing pack.
American Furyk carded rounds of 62 and 66 on Saturday to climb up the leaderboard after opening with a level-par round of 70.
He broke the course record with his second-round effort, which included seven birdies and an eagle, and he followed that up with six more birdies in his second round.
606: DEBATEThe organisers were hoping to fit 36 holes into Saturday's play following a first day wash-out, as the remnants of Hurricane Gustav blew through Missouri but 23 players were unable to finish their rounds.
When Villegas returned on Sunday he saved par from a bunker with a 15-foot putt on the 5th - his 14th, missed a 10-foot birdie putt at the 7th and then took the outright lead with a birdie on the par-five eighth.
He will play in the final group with Furyk and Kim, who also came back to complete a third-round 66.
Furyk was delighted to get through his two full rounds in one day as he looks for his first PGA tour victory of the year.
"I tried to pace myself all day, knowing we were going to be out there for 36 holes. My goal was to play two solid rounds," the 38-year-old said.
He covered the back nine of the second round in just 28 shots, finishing it off with five successive birdies, and he remained upbeat despite ending the day with a bogey at 18.
"I still walk away in a positive frame of mind. I went at the pin with a wedge and it didn't work out. It's easy to make a mental mistake when you're tired, when your mind wanders a little bit," he added.
KJ Choi shot a 64 to be level with Kim on nine under, but world number two Phil Mickelson could only card a 71 to finish seven shots off the lead.
Spain's Sergio Garcia headed the European challenge on five-under after a 69, but the highlight of his day came in the second round when he holed in one at the 205-yard 3rd with a five-iron.
Open and US PGA champion Padraig Harrington was over par for the second successive round and his 72 left him well out of contention on two over par.
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