Rory McIlroy tracked the flight of his drive as long as he could against the rain clouds over Valhalla on Friday, not quite sure where it landed. He turned to his caddie for confirmation and asked, "Was it good?"

"Beautiful," J.P. Fitzgerald replied, his eyes still fixed on a shot that traveled 311 yards right down the middle.

Such is the state of McIlroy's game at the PGA Championship.

He produced superior shots with his long game. He made all the right putts Friday in a round of 4-under 67. And even with a one-shot lead over Jason Day and Jim Furyk going into the weekend, there was an ominous feeling at the final major of the year.

"When I'm playing like this, it's obviously very enjoyable," McIlroy said. "I can't wait to get back out on the course again tomorrow and do the same thing all over again."

It used to be that way for Tiger Woods.

But on a day that McIlroy posted his 12th straight round under par, Woods hobbled away from Valhalla with a sore back and an uncertain future. He never came close to making the cut, and only a pair of late birdies kept it respectable. Woods had another 74 and missed the cut by five shots.

Oddly enough, McIlroy opened with the exact same scores (66-67) as Woods did 14 years ago at Valhalla when he barely outlasted Bob May in a playoff for his third straight major of the season on his way to an unprecedented sweep of golf's biggest events.

McIlroy, who was at 9-under 133, isn't nearly at that stage. He picked up his third major -- and the third leg of the career Grand Slam -- last month at Royal Liverpool in a wire-to-wire win at the British Open. He followed with a comeback victory last week at Firestone for his first World Golf Championship.

The biggest difference between Valhalla now and 14 years ago was the competition lined up behind McIlroy.

Furyk, a former U.S. Open champion who was runner-up last year at the PGA, got up-and-down from behind the green on the par-5 18th for birdie and a 68. Moments earlier, Day capped off the best round of a soggy day with a birdie on the 18th for a 65. Day has three runner-up finishes in the majors.

Right behind were Ryan Palmer (70) and Rickie Fowler (66), a runner-up in the last two majors. Not to be overlooked was Phil Mickelson, a five-time major champion who made eagle on the last hole for a 67 to get within three shots.

Even so, McIlroy is dangerous when he gets in the lead, especially at a major. He learned his lesson at Augusta National in 2011 when he tried to protect a four-shot lead and wound up shooting 80. He bounced back for an eight-shot win at the U.S. Open, won the PGA Championship by a record eight shots a year later and only last month went wire-to-wire to win the third leg of the career Grand Slam at the British Open.

"My mindset has stayed the same since that day at Augusta," McIlroy said. "If I'm two ahead going into the weekend here, I'm going to try to get three ahead. And if I'm three ahead, I'm going to try to get four ahead. ... I'm just going to try to keep the pedal down and get as many ahead as possible."

He didn't take his first lead until the par-5 18th hole, the midway point of his round.

McIlroy hit 4-iron to the front of the green, and his eagle putt rammed into the back of the cup as if it had nowhere else to go. It was a moment where the No. 1 player in the world looked as if he had just seized control of the PGA Championship.

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

He was reminded that winning majors isn't easy, even if he can make it look that way.

In sloppy conditions, McIlroy took bogey on the tough par-4 second hole, and then had to scramble for four straight pars. But on the par-5 seventh, after another big tee shot on the left side of the fairway, he hit a 5-wood over the water to 8 feet, a shot that reminded everyone why he's the class of golf. That was one of the few putts he missed -- he still made birdie -- and McIlroy finished with a 15-foot birdie on the final hole.

"When he hits the driver that straight and that long, and the short game is incredible, it's very difficult to beat him," U.S. Open champion Martin Kaymer said. "His iron shots, they are very solid. He doesn't miss many golf shots. So you just have to respect it a lot, how good he plays. There's nothing wrong with his game."

Fowler saw it during the final round at Royal Liverpool last month. He knows what kind of work is left for the guys chasing him.

It can be done. But they might need some help from McIlroy.

"He's the best player in the world right now," Fowler said. "And I would say a lot of that is his confidence right now with the way he's driving the ball. If he continues to drive it, he's going to continue to be in contention at a lot of golf tournaments and win a lot of times."

Maybe. But the final major is only at the halfway mark.

Day has been battling injuries to his wrist ever since winning the Match Play Championship, and he was pleasantly surprised to be in the hunt at another major. He is explosive, much like McIlroy, minus the experience of winning.

"I'm clearly not the favorite," Day said. "It's going to be tough to beat him. But then again, there's a lot of great golfers behind us that are in form, as well."