Kevin Kisner made four opening pars to establish a one-shot lead on day three of the US PGA Championship at Quail Hollow Club.
The American has never finished in the top ten at a Major Championship but entered Saturday in a share of the lead and looked unflappable as he stayed at eight under to sit a shot ahead of Japan's Hideki Matsuyama.
The World Number Three dropped a shot on the first - which nobody birdied in round three - to sit a shot ahead of Australia's Jason Day and American Chris Stroud.
South African Louis Oosthuizen was then at five under, two shots clear of Justin Thomas.
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 but in the group ahead Francesco Molinari had surrendered a double-bogey after going over the back in three and needing two putts.
Oosthuizen did brilliantly to save par on the second after seeing his tee-shot rest against a tree but looked to have hurt his arm in the process, while another dropped shot left Molinari six off the lead.
Day was moving in the other direction and a stunning approach to four feet on the second helped move him to seven under but he gave the shot straight back on the next.
Stroud and Oosthuizen were both level par for the day after four holes, with Thomas also level for his round after five.
Byeong-hun An was then at two under alongside Rickie Fowler and Paul Casey, with Molinari in the group a shot further back after another bogey on the third.