Right when it looked as though McIlroy had no serious challenge Sunday, Tiger Woods came on strong with a birdie-eagle finish for a 62 — his lowest final round ever — to get within one shot of the lead.
McIlroy could hear the roar from the farthest corner of PGA National, and the 22-year-old from Northern Ireland responded with some clutch golf of his own. He made an 8-foot birdie putt, and then made three clutch par saves during a daunting stretch at PGA National.
He played it safe with a two-shot lead on the par-5 18th and made par to close with a 1-under 69 and the victory he needed to replace Luke Donald atop the world ranking that will be published Monday.
"It was tough today, especially seeing Tiger make a charge," McIlroy said. "I knew par golf would probably be good enough. To shoot 1 under in these conditions, when you go into the round with the lead, is very nice. And I was just able to get the job done."
McIlroy is the 16th player to be No. 1 in the world, and the second-youngest behind Woods, who was 21 when he first went to No. 1 after the 1997 U.S. Open.
Donald responded quickly to the victory, tweeting "Congrats @McIlroyRory enjoy the view!"
Woods made two eagles in the final round and wound up two shots behind, along with Tom Gillis, who birdied the last hole for a 69.
McIlroy, who finished on 12-under 268, won for the fifth time in his career. Three of those are on the PGA Tour, including his record-setting victory in the U.S. Open last summer at Congressional.
He has finished out of the top five only once since the PGA Championship last August.
"There's very few players as good at him at his age out there winning tournaments," three-time major champion Padraig Harrington said. "There are guys with potential, but he's already delivered. And he has a good balance in his life. He doesn't look like a guy who is going to burn out. He looks like he's going to be here for a while."
McIlroy shared a big hug with his father, Gerry, as he walked off the 18th green. His parents have come over from Holywood to stay with him in southern Florida through the Masters, where McIlroy figures to be a top favorite.
After a Sunday like this, no one will be quick to rule out Woods.
He was nine shots behind going into the final round, and even a 31 on the front nine in blustery conditions left him five shots behind McIlroy. But the finish — especially that 5-iron onto the 18th green — was vintage Woods, and it at least gave him a chance.
"To me, it was the old Tiger back, the guy that I remember," said Ernie Els, who played alongside him. "He never missed a shot or made a bad swing."
Lee Westwood, playing two groups ahead of Woods, closed with a 63 to finish alone in fourth.
"It was a lot of fun out there," Graeme McDowell said. "It was just roars going up all over the golf course. For Rory to go out today with a two-shot lead and have Tiger shoot 62 on him and Westwood shoot 63, it just shows how hard it is to win golf tournaments on any tour in the world, but especially this tour.
"This golf season just got a lot more spicy."
McIlroy wasn't at this best on the front nine, though he did what the best players tend to do by turning a suspect round into a decent score. Despite having only two reasonable birdie chances on the front nine — he made one of them — McIlroy saved himself with a pair of par putts from 12 feet and another one from 8 feet.
No one looked capable of catching him.
Woods was still five shots behind until a finish that served as a reminder why this guy can't be counted out — not at PGA National, certainly not with the Masters around the corner.
"I figured I had to go birdie-birdie to have a chance," Woods said.
He did one better.
First, Woods dropped a 25-foot birdie putt on the 17th hole, followed by a big tee shot on an aggressive line that left him a 5-iron into the par-5 18th, with the pin tucked over a bunker to the right side of the green near the water. Woods said it reminded him of his famous shot on the 18th at Glen Abbey in the 2000 Canadian Open, a 6-iron out of a bunker and over the water to a tight pin.
This one cleared the sand and settled 8 feet away, and Woods swept his fist when it dropped for eagle.
He finished at 270, his lowest 72-hole score since he had a 265 at the 2009 BMW Championship, his last PGA Tour win.
The roar from thousands of fans down the 18th fairway could be heard at every corner of PGA National, yet it didn't rattle McIlroy. Moments later, he holed an 8-foot birdie putt on the 13th to build his lead back to two shots.
From there, it was a matter of hanging on.
With so much emphasis on his swing, the final hour was all about his will. After making his first birdie on the eighth hole, McIlroy had a two-shot cushion for most of the final round. But there was something different about having someone — especially Woods — in the clubhouse at 10 under, with McIlroy facing six holes and a shrinking margin of error.
He was 65 feet from the hole in rough so deep he had trouble finding his ball when McIlroy gouged out a wedge to 4 feet for par. In the back bunker on the par-3 15th, facing a shot that ran away from him toward the water, he blasted out to 6 feet and made another clutch par putt.
His final act was from another bunker on the par-3 17th, and he saved par again. McIlroy had seven one-putt greens (another was a birdie from the fringe), and one-putted four of the last six holes.
"My short game all week has been very good, and it's what you need on a tough golf course like this," McIlroy said. "I was able to do that, especially on 15 and 17. I needed to make pars there. My short game felt good all week, and it definitely saved me today."