Rory McIlroy made golf look ridiculously easy again on Thursday, but he was expecting to have to work a lot harder on his return to Kiawah Island on Friday.

One behind US-based Swede Carl Pettersson after starting the USPGA Championship - golf's final major of the year - with a five-under-par 67, McIlroy was in no mood to make any bold predictions.

"We know that there's going to be a bit of wind coming in and maybe a bit of bad weather," the 23-year-old Northern Irishman said. "It's just something that you're going to have to deal with and I'm just happy that I got off to a great start - I have a great platform to go from."

He added: "Hitting balls on the range there was completely no wind. It was flat calm and I really thought that I had to take advantage of the conditions.

"I'm pretty comfortable on the golf course. I played nine holes on Monday, nine holes on Tuesday and that was it.

"I didn't feel like I needed to play any more. I've got my lines off the tees and I know what it's like around the greens."

Alongside McIlroy are another Swede, Alex Noren, Spanish Ryder Cup hopeful Gonzalo Fernandez-Castano and big-hitting American Gary Woodland. Graeme McDowell was handily placed on four under - part of a group which also included Adam Scott, the Australian who blew the Open last month with four closing bogeys.

Tiger Woods, Justin Rose and Wales' Irish Open champion Jamie Donaldson shot 69s, while Ian Poulter and 2008 champion Padraig Harrington - both looking to move into a Ryder Cup qualifying place - had 70s.

Two late birdies helped Martin Laird to a one under 71, but Luke Donald was in the water on the 17th as he shot 74 and Lee Westwood also finished poorly and signed for a 75.

Former Open champions Darren Clarke and Paul Lawrie both had 73s like Simon Dyson and David Lynn, while Robert Rock took 76 and Paul Casey, with only one cut made since dislocating his shoulder snowboarding last Christmas, struggled again and handed in a 79.