Rory McIlroy went from shocked and annoyed to being delighted with his mental strength after the first round of the US PGA Championship at Valhalla.

World number one McIlroy ran up a double-bogey seven on the 10th after hooking his second shot out of bounds and then three-putted the 11th, but responded with four birdies in succession and narrowly missed several good chances before carding another on the 18th.

That gave the Open champion, who is seeking his third win in succession and a fourth major title, a five-under-par 66, one shot off the lead shared by Lee Westwood, Ryan Palmer and Kevin Chappell.

"It could have been a couple better if those last few putts had dropped but 66 is a solid start" - Rory McIlroy

"I was really annoyed," the 25-year-old said. "The second shot on 10 was actually a bit of a shock, it's the worst shot I have hit the last few weeks.

"It came out of the blue and knocked me off track but to come back the way I did was great. I really needed that and it shows mentally where I am at with my game.

"Things like 10 happen, you hit bad shots like that every now and then and I was really annoyed with myself to bogey the next hole as well. After I hit that second shot on 12 I started to give myself a 'C'mon, that was better' and that sort of kick-started things."

"It could have been a couple better if those last few putts had dropped but 66 is a solid start."

McIlroy began the week as a 5/1 favourite to win the US PGA for the second time in three years, but vowed to keep focused on the task at hand and avoid the hype surrounding his superb recent form.

"I know where my game is at and I am very confident with it," he added. "I am really happy with everything, I have a good thing going and am just trying to ride the momentum as much as I can.

"I'll try to read as little as possible. I have three more rounds to play and hope they are as good as they were today.

"I'm driving the ball fantastically well and I'm really happy with it. The fairways this week are a little more generous than they were last week so I feel like I can step up on these tees and hit it just as far."