"I played well all day," Westwood said. "I got off to a nice, steady start. Hit a lot of good shots. Hit a lot of fairways. Putted very nicely and just really carried on from the final round last week."
Westwood shot a final-round 63 at last week's WGC-Bridgestone Invitational. He arrived at Valhalla feeling good about his game.
"That obviously gave me some confidence coming into this week," he said. "Just tried to sort of almost take it easy in the practice rounds. Played nine holes each day. Didn't want to drain myself, especially with the heat."
Except for the Englishman's game, it wasn't too hot today at Valhalla, with temperatures in the low 80s due to cloud cover. Rain is in the forecast, which could send scores lower.
Kevin Chappell, who said, "I guess I was in a good rhythm out there," also posted a 65. Chappell, 28, a UCLA product, is playing in his second PGA Championship. Last year he missed the cut at Oak Hill. His first round at Valhalla included six birdies and no bogeys.
"I think if you're driving it long and straight, any course plays to your game," Chappell said, "and that's the key to this golf course ... getting the ball in play and being able to attack these short holes."
Ryan Palmer, who was part of the afternoon wave, also finished with a 65.
Other select scores:
66 - Jim Furyk, Edoardo Molinari
68 - Ian Poulter
69 - Rickie Fowler, Phil Mickelson, Nick Watney, Jason Day, Jimmy Walker, Victor Dubuisson, Jamie Donaldson
After an opening 3-over 74, Tiger Woods has some work to do if he wants to play on the weekend. A "dialed in" golf swing on the range went missing during his first round.
"Unfortunately, I didn't carry it to the golf course," Woods said.
Tiger also struggled with his speed on Valhalla's putting surfaces.
"I didn't get a putt to the hole."
Paired with Tiger, Phil Mickelson started poorly but finished strong, playing the last 10 holes in 4 under par.
"It's been a while since I felt like my game was to this point," Mickelson said after his 69.
Players are still on the golf course, including Rory McIlroy, who is at 4 under on the 16th hole.
Defending champion Jason Dufner pulled out after 10 holes because of neck problems. Dufner was 8 over par.
"I've been feeling pretty bad all week," Dufner said. "I felt bad last week. I haven't made a birdie in 45 holes and I'm just not able to play golf right now. I tried to do what I could to be able to compete some and give it a go, but it is just pointless."