Kevin Kisner turned in 29 to storm into a one-shot lead early on day two of the US PGA Championship at Bellerive Country Club.
The American held the 54-hole lead at this event last season before finishing in a tie for seventh and achieved his best finish in a Major last month when he finished in a tie for second at the Open.
His blistering first nine in St Louis moved him to nine under, one shot clear of countryman Gary Woodland and three ahead of South African Brandon Stone.
Rickie Fowler was among the later starters at five under, a shot clear of a group of seven players including Race to Dubai Rankings presented by Rolex Leader Francesco Molinari.
Kisner started the day three shots off the lead but hit a lovely appraoch into the first to edge closer to the front.
Stone began his round with six pars but a 20-footer on the 16th had him within one before a nice chip from Woodland on the par four 11th - which had seen the tee moved up and measured just 297 yards - handed him a two-shot lead.
Playing partner Kisner drove the green on the same hole to join Stone but the 25 year old took advantage of the 17th to move back within one of the lead.
Kisner put his tee-shot to four feet on the 13th to get to six under and that was just one clear of Italian Molinari who was making a move.
The Open champion chipped in on the tenth for a birdie and then holed from ten and seven feet on the 12th and 14th to get to five under.
Woodland needed three goes to get down from the fringe on the 14th to make it a three-way tie but Stone soon dropped out of that group with a bogey on the first.
A Kisner approach to ten feet on the 15th edged him ahead but Woodland hit a stunning second into the 17th to leave himself five feet for eagle and jump into the lead.
Kisner followed him in for a routine gain, and an approach to 15 feet on the next handed the South Carolina native the lead at the turn.
Stone then hit a lovely approach to the fourth to get back to six under, while Molinari dropped a first shot of the day after three-putting the 18th to drop into an intimidating group five off the lead alongside playing partner Brooks Koepka, more Major winners in Justin Rose, Zach Johnson and Adam Scott, American Patrick Cantlay and Chilean Joaquin Niemann.