Springfield - Unheralded Robert Streb matched the record-low round in major golf history on Friday with an astonishing seven-under par 63 to seize a share of the lead after the second round of the PGA Championship.
Top-ranked defending champion Jason Day's amazing run of seven birdies in eight holes to grab a share of third was overshadowed by a 29-year-old American on a rain-soaked Baltusrol layout soggy enough to surrender low scores in a wild afternoon of shot making.
Back-nine starter Streb made a lone bogey and eight birdies, the last of them on a curling 21-foot putt at the par-three ninth to make history and match compatriot Jimmy Walker for the 36-hole lead at nine-under 131.
"I was pretty excited about it," Streb said. "I was waiting on it to break, waiting on it to break and it finally turned there at the end.
"It was a great round. Happy to be part of that 63 club."
Streb's 63 was the 30th shot at a major but he was the 28th player to achieve the feat, Fiji's Vijay Singh and Australian Greg Norman having done it twice. British Open champion Henrik Stenson and runner-up Phil Mickelson each did it two weeks ago at Royal Troon.
Baltusrol has surrendered the most 63s of any major course with four, including two of only four in US Open history, the 63s of Jack Nicklaus and Tom Weiskopf in the first round in 1980, and another by Thomas Bjorn at the 2005 PGA Championship.
Streb, whose lone US PGA victory came in the 2014 McGladrey Classic, has gone 27 US PGA events without a top-10 showing since placing 10th at the 2015 PGA Championship, although he was fourth at this year's European Tour Nedbank Challenge in South Africa.
Streb missed the cut in all three prior majors this year but played the round of his life to put himself in contention for a major title.
"The ball-striking and putting has been a little difficult this year," he said. "Just been trying to hang on by a thread. Obviously it's coming together this week, which is nice."
Australia's Day fired a 65 to stand two strokes adrift on 133 along with Argentine rookie Emiliano Grillo, who shot 67.
Day, who battled illness and fatigue in round one, became annoyed at a double-bogey on the seventh hole and responded with short birdie putts at eight and nine, 18-foot birdie putts at 10 and 13 around a 10-footer at the par-3 12th.
Then came a stunning 37-footer at 14 and a five-footer on 15 for good measure, although he failed to take advantage of the par-5 17th and 18th or he might have shot 63, or better.
"That double bogey kicked me in the bum a little bit," Day said. "A little disappointed I didn't birdie either of the par-5s. But I'm saving them for the weekend.
Morning showers dumped an inch of rain on the 7,428-yard layout and halted play for 41 minutes as groundskeepers cleared puddles from greens and standing water from fairways. Balls held on saturated greens and made up for the lack of fairway roll.
"It was much softer," Walker said. "If you were in the fairway you could do anything you wanted with the golf ball."
Sweden's Stenson was alone in fifth after his second consecutive 67 with two-time major winner Martin Kaymer of Germany sharing sixth on 135 with Americans Patrick Reed and Brooks Koepka.
Japan's Hideki Matsuyama eagled the second hole on his way to a 67 to share ninth with Welshman Jamie Donaldson and Americans Rickie Fowler and Harris English.
Fourth-ranked Rory McIlroy fired a 69 but could not overcome a bogey-less first-round 74 and the four-time major champion missed the cut on 142 by a stroke.
US left-hander Mickelson, who opened with a triple bogey after a tee shot that went over a fence and onto a street, birdied the last to make the cut on the number.
Second-ranked Dustin Johnson, who won the US Open last month, fired a 72 to finish on 149. Only 10 players had worse 36-hole totals.
The PGA of America apologised after a rules blunder that impacted the first back-nine starters, including Japan's Yuta Ikeda, who shot 67 to stand on 137.
The location guide sheet given Ikeda's group showed a hole cut on the left side of the green when it had actually been put on the right side, a blunder not caught until the group had played approaches at the 10th, which Ikeda bogeyed.
Also on 137 was Jordan Spieth, whose shot from a gravel path at the seventh hole aroused ire for television viewers over possible rules violation, although a PGA of America statement said there was no violation.
Scores on Friday from the second round of the 98th PGA Championship at par-70 Baltusrol Golf Club (USA unless noted):
131 - Jimmy Walker 65-66, Robert Streb 68-63
133 - Emiliano Grillo (ARG) 66-67, Jason Day (AUS) 68-65
134 - Henrik Stenson (SWE) 67-67
135 - Martin Kaymer (GER) 66-69, Patrick Reed 70-65, Brooks Koepka 68-67
136 - Hideki Matsuyama (JPN) 69-67, Harris English 67-69, Rickie Fowler 68-68, Jamie Donaldson (WAL) 69-67
- Yuta Ikeda (JPN) 70-67, William McGirt 70-67, Daniel Summerhays
70-67, Jordan Spieth 70-67, Zach Johnson 71-66, Billy Hurley 72-65, Adam
Scott (AUS) 70-67, Hideto Tanihara (JPN) 71-66, Gregory Bourdy (FRA)
138 - John Senden (AUS) 68-70, Alex Noren (SWE) 70-68, Webb
Simpson 69-69, Louis Oosthuizen (RSA) 68-70, Jon Curran 69-69, K.J. Choi
(KOR) 68-70, David Lingmerth (SWE) 68-70, Branden Grace (RSA) 70-68,
Paul Casey (ENG) 69-69, Scott Hend (AUS) 68-70, Andy Sullivan (ENG)
67-71, Ryan Moore 71-67
139 - Steve Stricker 69-70, Andrew
Johnston (ENG) 70-69, Danny Lee (NZL) 69-70, Song Young-Han (KOR) 71-68,
Tyrrell Hatton (ENG) 71-68, Lee Westwood (ENG) 69-70, Brandt Snedeker
73-66, Marcus Fraser (AUS) 71-68, Soren Kjeldsen (DEN) 70-69, George
Coetzee (RSA) 72-67, Jhonattan Vegas (VEN) 68-71, Vaughn Taylor 68-71,
Kevin Na 71-68, Ross Fisher (ENG) 66-73
140 - Russell Henley
68-72, Marc Leishman (AUS) 71-69, Russell Knox (SCO) 70-70, Cameron
Tringale 72-68, Bubba Watson 71-69, Kyle Reifers 70-70, Bradley Dredge
(WAL) 69-71, Daniel Berger 71-69, Aaron Baddeley (AUS) 70-70, Kevin
Kisner 71-69, Brian Stuard 70-70, James Hahn 67-73, Bill Haas 70-70
- Rich Beem 69-72, Thomas Pieters (BEL) 71-70, Francesco Molinari (ITA)
71-70, Jim Furyk 74-67, Danny Willett (ENG) 71-70, Justin Thomas 69-72,
Padraig Harrington (IRL) 71-70, Keegan Bradley 73-68, Phil Mickelson
142 - Colt Knost 69-73, Ryan Palmer 71-71, Billy Horschel
72-70, Jason Dufner 71-71, Kiradech Aphibarnrat (THA) 70-72, Thongchai
Jaidee (THA) 72-70, Joost Luiten (NED) 72-70, Matthew Fitzpatrick (ENG)
72-70, Justin Rose (ENG) 70-72, Charl Schwartzel (RSA) 73-69, Freddie
Jacobson (SWE) 71-71, Patton Kizzire 71-71, Jason Kokrak 70-72, Ernie
Els (RSA) 73-69, Rafael Cabrera-Bello (ESP) 72-70, Matt Jones (AUS)
74-68, Roberto Castro 72-70
Missed the cut:
143 - Yang
Yong-Eun (KOR) 72-71, Scott Piercy 72-71, Luke Donald (ENG) 72-71, Chris
Kirk 74-69, Chris Wood (ENG) 69-74, Victor Dubuisson (FRA) 69-74, Rory
McIlroy (NIR) 74-69, Ryan Helminen 72-71, Smylie Kaufman 73-70
- Harold Varner 72-72, Thorbjorn Olesen (DEN) 70-74, Brendan Steele
71-73, An Byeong-Hun (KOR) 72-72, Kim Si-Woo (KOR) 71-73, J.B. Holmes
75-69, Vijay Singh (FIJ) 74-70, Rikard Karlberg (SWE) 72-72, Rod Perry
73-71, Zac Blair 73-71
145 - Gary Woodland 73-72, Kevin Chappell
72-73, Bryce Molder 74-71, Shane Lowry (IRL) 72-73, Sergio Garcia (ESP)
71-74, Ben Polland 72-73, Kevin Streelman 75-70, Darren Clarke (NIR)
74-71, Jason Bohn 71-74, Matt Dobyns 73-72, Charley Hoffman 75-70
- Bernd Wiesberger (AUT) 75-71, Peter Malnati 73-73, Rich Berberian
72-74, Anirban Lahiri (IND) 73-73, Matt Kuchar 74-72, Mark Brown 75-71,
Kristoffer Broberg (SWE) 72-74, Jonas Blixt (SWE) 75-71
147 - Rob
Labritz 71-76, David Toms 74-73, Lee Soo-Min (KOR) 77-70, Tony Finau
77-70, Brian Gaffney 74-73, John Daly 74-73, Jamie Lovemark 71-76, David
148 - Michael Block 72-76, Johan Kok 72-76, Fabian
Gomez (ARG) 75-73, Jim Herman 77-71, K.T. Kim (KOR) 77-71, Wang
Jeung-Hun (KOR) 73-75, Josh Speight 77-71, Nicolas Colsaerts (BEL)
72-76, Greg Chalmers (AUS) 72-76
149 - Joe Summerhays 76-73, Troy Merritt 77-72, Rocco Mediate 76-73, Dustin Johnson 77-72, Graeme McDowell (NIR) 74-75
150 - Brandon Stone (RSA) 79-71, Mitch Lowe 74-76, Tommy Sharp 77-73, Omar Uresti 72-78
151 - Brad Ott 79-72, Shaun Micheel 77-74
152 - Wyatt Worthington 76-76
154 - James Morrison (ENG) 78-76, Rick Schuller 78-76
157 - Brad Lardon 83-74