Rory McIlroy finishes at 9 under

LOUISVILLE, Ky. -- If there is such a thing as a poor round of 67, that is how it looked for Rory McIlroy on Friday.

Perhaps the standards have risen to such a level, but McIlroy's 4-under-par effort was not the comfortable stroll around Valhalla Golf Club that he seemingly had during the opening round of the PGA Championship. But he birdied his final hole nonetheless and took an early 36-hole lead.

McIlroy's 67 put him at 133, 9-under par, one stroke better than Jason Day, who shot a 6-under 65 -- the low round of the day -- on Friday. Ryan Palmer and Rickie Fowler are two strokes back.

"I scored well, but the golf wasn't quite as pretty as yesterday at times," McIlroy said. "Neither was the weather, obviously. Played well for the most part. There were some key up-and-downs to keep the momentum going in the round."

McIlroy had an eagle, four birdies and two bogeys during a rain-soaked second round that was interrupted for 50 minutes in the morning. Players returned to the course despite heavy rains at times, and the round continued into the afternoon.

Regardless of the conditions, McIlroy is playing some of the best golf of his career of late. He won his previous two starts, at the Open Championship and WGC-Bridgestone Invitational. In his past 10 competitive rounds, he is a combined 41 under.

"I'm in a really solid place in terms of not getting ahead of myself on the golf course," said McIlroy, 25. "Staying in the present. I've got a couple little trigger words that I'm using, and that seems to be getting me through. I can't really explain it any better than that.

"Obviously my swing is technically in a good place at the minute. I'm able to shape the ball in both ways. I'm confident, and I'm just on a good run. You've seen when I've been on good runs like this. I can sort of keep it going for a little while. Hopefully I can keep it longer than I have done in the past."

McIlroy did have his moments, however. Starting on No. 10, he failed to birdie the par-5 hole, then bogeyed the 12th before birdies at the 13th and 15th and an eagle at the 18th, where he rolled in a 30-foot putt.

Another bogey at the second hole dropped him out of the lead, and he missed an eagle putt from 8 feet at the seventh before also birdieing the ninth.

It wasn't as tidy as his opening-round 66 -- McIlroy hit eight of 14 fairways on Friday compared to 12 on Thursday, and hit 11 greens after hitting 13 in the opening round. But it worked.

McIlroy is attempting to become the first player to win back-to-back majors since Padraig Harrington won the Open Championship and PGA Championship in 2008.

His play is impressing many players, including Ian Poulter, who took to Twitter before he began his round Friday to salute the 25-year-old.

Rory is on a mission, he is playing simply incredible golf at the moment. Need to find a gear to step it up.

- Ian Poulter (@IanJamesPoulter) August 8, 2014Among active players, only Tiger Woods (14), Phil Mickelson (five) and Ernie Els (four) have more than the three majors won by McIlroy.

"It would be big," McIlroy said. "It would be a fourth major championship, two in one year, two in a row. It would be big. There's a lot of golf left to play, and I'm going to try my best to just keep what I've got and keep doing that.

"If I was sitting here on Sunday night with the Wanamaker [Trophy] right here, I'd be very happy."