Robert Streb, who has not had a US top-10 finish in a year, matched the record-low round in major golf history on Friday with a seven-under par 63 at Baltusrol to seize a share of the lead at the PGA Championship.
The 29-year-old American began on the back nine and made eight birdies, the last of them on a 21-foot putt at the par-three ninth to match compatriot Jimmy Walker for a share of the 36-hole lead at nine-under 131.
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 the Nedbank Challenge in South Africa on the European Tour.
He 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. Top-ranked defending champion Jason Day shared third with Argentina's Emiliano Grillo on 133.
The Australian's round of 65 included a run of seven birdies in eight holes. British Open champion Henrik Stenson of Sweden 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.