South Africa's Branden Grace eased to the top of the leaderboard as Kiawah Island continued to pose a tough test on day two of the 103rd US PGA Championship.
As overnight leader Corey Conners battled to remain in contention, Grace took advantage of the two par fives on the front nine of the Ocean Course to reach the turn in 34.
And the 33-year-old, who holds the record for the lowest score in a men's major following his 62 in the 2017 Open, then increased his lead in style by holing out from a bunker for a birdie on the 10th.
At five under par, Grace enjoyed a two-shot lead over compatriot Christiaan Bezuidenhout and American Kevin Streelman, with later starters Brooks Koepka, Keegan Bradley and Viktor Hovland also on three under.
Conners had begun the day on five under after a superb opening 67, but carded five bogeys and two birdies in his first seven holes and made his first par of the day on the fearsome 17th.
That hole cost Jon Rahm a double bogey after he found the water off the tee, the fiery Spaniard throwing his club in disgust and then threatening to snap another after also dropping a shot on the 18th.
Europe's Ryder Cup captain Padraig Harrington was enjoying a much calmer round, the 2008 champion posting two birdies and one bogey in his first 11 holes to improve to two under.
But the best round of the day so far was coming from someone Harrington has earmarked for a wild card for September's contest at Whistling Straits, Ian Poulter making an eagle and two birdies on the front nine to reach one under.
The halfway cut was projected to fall at two over par, meaning Rory McIlroy had his work cut out to make the weekend following his opening 75.
McIlroy won by eight shots at Kiawah in 2012 but since 2015 is a combined 35 over par in the first round of major championships and again faces an uphill task to win a fifth major title and first since the 2014 US PGA.