Kevin Kisner shot a six under par 64 to sit at 9 under par, one shot out of the lead. "It's very warm out here so I definitely need a change of clothes and a shower and a freshen up, then I'll come back out and get ready to go".
After opening his day with a gain at the par-five eighth he dropped back to two-under with an immediate bogey at the next but a flawless back nine, including a late birdie at the par-five 17th moved him into contention.
Competition will resume at 7 p.m. (1200 GMT) with about 3 1/2 hours of play to complete before making the cut.
Dustin Johnson, the world's No 1 player, had a 66 and joined Schwartzel and Thomas Pieters (66) at 133. "This golf course is stacked right now and everyone is bunched". "I'm not too anxious with what anyone else is doing out there".
Kisner, Koepka and South African Charl Schwartzel each flirted with the lowest all-time major round of 62 fired by South Africa's Branden Grace in the third round of last year's British Open at Royal Birkdale.
Woodland had a four-under 66 and set the PGA Championship record with a 36-hole score of 130.
Lowry has had an up and down season thus far, sitting outside the top 150 in the FedEx Cup ahead of this final major of the year, but Lowry has made a few changes in recent weeks and now has his brother Alan on the bag, which appears to be working well.
"I feel safe because I feel safe where my game is, " he said.
"But it was a big thing for me to hole than and go on to make a couple of birdies from there". I didn't even think of it. "I didn't know that was such a rivalry".
Koepka defended his US Open crown in June, the first back-to-back US Open victor since Curtis Strange in 1988-89. He was at 7 under, three shots behind Woodland with eight holes to play. He had to two-putt from 50 feet at the 15th and also from 90 feet at the 18th.
"I'm in a lot better position than I was when I came out here this morning, which is great", Thomas said.
"Putts like that are huge, weeks like this, but it was a straightforward putt, it was seven feet and it was right edge up the hill, it is the putt you want to leave yourself, and it was clever with the chip shot".
After a par at the fourth, Woods hit a booming 318-yard drive into the fairway at No. 5, then stuck an approach shot to inside of 10 feet.
"It's been 16 pars in a row from yesterday to today, so hopefully I can break that run in the morning", McIlroy said.
When he walked off the course, Koepka's two-day total of eight-under 132 was two behind the 10-under pace set by Gary Woodland.
"He's rolling the rock and really striping it", Kisner said.
Woodland has never finished better than 12th in 27 major starts but he has never started so well in one either. I felt like I was putting for birdie pretty much every hole.
Eighth-ranked Jordan Spieth can complete a career Grand Slam with a victory this week, but the 25-year-old American shot 67 to stand on 137.