Kevin Kisner picked up a single shot on the front nine to hold a one-shot lead on day three of the US PGA Championship at Quail Hollow Club.
The American entered Saturday in a share of the lead and took advantage of the par five seventh to get to nine under and sit a shot ahead of countryman Chris Stroud and Japan's Hideki Matsuyama.
Stroud picked up two shots in his first nine holes while the World Number Three made the turn in level par.
South African Louis Oosthuizen was then at five under alongside 2015 champion Jason Day.
Matsuyama was left with a difficult angle into the first off the tee and dropped a shot and it was almost a two-shot swing as Kisner saw a double-breaker agonisingly graze the hole.
Day did well to get up and down from a greenside bunker to save par and ahead on the second Oosthuizen did brilliantly to save par after seeing his tee-shot rest against a tree but looked to have hurt his arm in the process.
A stunning approach to four feet on the second helped Day move to seven under but he gave the shot straight back on the next.
Stroud also got to seven under as he holed from 18 feet on the fifth but he gave the shot back as he missed the green on the par three next before taking advantage of the seventh.
Oosthuizen saw the trainer and had strapping put on his arm before missing the green and bogeying the sixth but, just like playing partner Stroud, he bounced back on the seventh.
Day had eagled the seventh on days one and two but three-putted for par and that saw him lose ground as Kisner just avoided the water and got up and down for birdie, with Matsuyama picking up a shot after getting on in two.
Stroud then joined Matsuyama at eight under as he holed from 12 feet on the eighth and the Japanese did well to save par on the ninth after hitting his drive into the trees.
Day did not do so well and when he failed to get up and down from a greenside bunker he was four shots off the lead.
Rickie Fowler and Justin Thomas were then four under after ten holes, a shot clear of Paul Casey and Scott Brown.
Francesco Molinari and Gary Woodland were two under.