South Korea's Kim Si-woo will take a slender one-shot advantage into the final round of the Valero Texas Open after a birdie on the 18th hole left him within sight of a wire-to-wire victory on Saturday.
Kim, who had started the day four shots clear, had gradually been reeled in by Canada's Corey Conners as he struggled to adjust to steady rain and gusty winds at TPC San Antonio's AT&T Oaks Course.
However the 23-year-old from Seoul steadied himself on the back nine, and delivered a birdie on the long par-five 18th to post a three-under-par 69 to move one shot clear of the field heading into Sunday's final round at 15 under.
"It was a tough day, rain and wind early on," said Kim. "But the weather got better and I played better. I felt a little bit of pressure but it feels great and I'm looking forward to tomorrow."
Conners meanwhile put himself into contention after carding a six-under-par 66 which left him at 14 under after 54 holes.
Conners, who is yet to taste victory on the PGA Tour, could complete a remarkable week on Sunday if he is able to claim the his first title.
The 27-year-old is only playing in San Antonio this week after battling through qualifiers last Monday, winning a six-way playoff to book his place in the field.
A win on Sunday would leave Conners $1.35 million richer, and earn him a ticket to next week's Masters in Augusta.
"I've managed my game really well, struck the ball really solidly, got myself out of trouble," Conners said. "It's a tricky golf course and ball striking is really important. I feel like I've been really solid with all of that."
Conners and Kim spent most of the day locked in a duel for the lead.
Early on, Kim could only watch as the birdies dried up and Conners chipped away at his lead with five birdies and four pars over the front nine.
After opening with a bogey, Kim could only make two birdies before the turn to leave him locked with Conners down the stretch.
A birdie on the par-four 10th moved Kim to 14 under overall while Conners could only bogey.
Conners reeled off back-to-back birdies on the 11th and 12th to move to six under for the day, and although a bogey on the 15th threatened to check his progress, a birdie on the par-three 16th kept him at 14 under.
Kim, who had aced the par-three 16th on Friday, was left kicking himself after missing a short birdie putt which would have given him sole possession of the lead. However he recovered with a birdie on the 18th to ensure a slender advantage ahead of the final round.
Kim and Conners will have little margin for error on Sunday, however, with a crowded leaderboard lurking just off the pace.
Leading the chase behind is Charley Hoffman, who produced the best round of the week on Saturday with an eight-under-par 64, 13 under overall after 54 holes.
Three players are two shots behind Hoffman on 11 under -- Venezuela's Jhonattan Vegas, Lee Kyoung-hoon of South Korea and Scott Brown.
But there was disappointment for three-time major winner Jordan Spieth. Spieth endured a Jekyll and Hyde round, making two bogeys and two double bogeys over the front nine to reach the turn at six over for the day.
Spieth however shrugged off that disastrous start to make five birdies over the back nine including a birdie-birdie-birdie finish to claw his way back to seven under, eight off the pace.