Brendon Todd clung to a one-stroke lead after Saturday's third round of the WGC St. Jude Invitational with South Korea's An Byeong-hun, Justin Thomas and Phil Mickelson making a charge.
Todd, trying to win his third title of a coronavirus-interrupted 2019-20 PGA season, scrambled to a one-under par 69 to stand on 12-under 198 for 54 holes at TPC Southwind in Memphis, Tennessee.
"I was battling my swing a little bit," Todd said. "But I'm excited to be in this position and feel like if I can go out there and swing a little better and keep this putting momentum going, I'll be in good shape."
An, still chasing his first US PGA victory, answered a double bogey at 11 with birdies on four of the last six holes to shoot 66 and reach 199 to join the American in Sunday's final duo.
American Rickie Fowler was third on 200 with defending champion Brooks Koepka, seeking a third straight PGA Championship title next week, fourth on 201 and Thomas fifth on 202 after a 66.
"I've just been playing consistently," Thomas said. "Bodes well for next week."
Fifty-year-old Mickelson shot 66 to join a pack in sixth on 203 that included South African Louis Oosthuizen, England's Matthew Fitzpatrick and American Chez Reavie.
"I can feel my game turn around. I'm starting to play well again," said Mickelson. "I'm starting to putt well and starting to drive the ball well and it just feels good. I think the results are going to start to slowly come back."
England's Tom Lewis matched a course record with a 61, equaling the mark set by Jay Delsing in 1993 and tied by Bob Estes in 2001.
Todd won PGA titles last November in Bermuda and Mexico after having slid outside the world rankings top 2000 in 2018, missing 37 of 40 cuts and flirting with retirement before finding his form again to make an astounding revival this season.
"For me it's just kind of hit the reset button, go out tomorrow, be Brendon Todd and play my best," the 35-yar-old American said.
Todd, who led by two when the day began, opened with a 14-foot birdie putt, took a bogey when he missed the fairway and green at the par-4 fifth and birdied the par-3 eighth on a 22-foot putt.
But he struggled with three bogeys and three birdies on the back side, the highlights being a 15-foot birdie putt at the par-4 12th and a birdie at the par-5 16th after sending his second shot into a greenside bunker.
He blasted out and sank a 16-foot birdie putt only to bogey 17 and miss a seven-foot birdie putt ahead of parring the last.
It was enough to hold back playing partner An, who birdied the 13th through 16th holes, starting the run with a 14-foot birdie putt and following with three more inside 3.5 feet. He also sank a clutch 10-foot par putt at the 18th.
Fowler led briefly after going 3-under on the front nine but bogeys at 11 and 17 left him two adrift.
198 - Brendon Todd 64-65-69
199 - An Byeong-hun (KOR) 68-65-66
200 - Rickie Fowler 64-67-69
201 - Brooks Koepka 62-71-68
202 - Justin Thomas 66-70-66
203 - Phil Mickelson 67-70-66, Louis Oosthuizen (RSA) 68-67-68, Matthew Fitzpatrick (ENG) 70-64-69, Chez Reavie 66-67-70
204 - Christiaan Bezuidenhout (RSA) 71-69-64, Joel Dahmen 72-67-65, Shane Lowry (IRL) 68-69-67, Tom Lewis (ENG) 73-70-61, Webb Simpson 69-66-69, Jason Day (AUS) 68-67-69, Im Sung-jae (KOR) 67-68-69