Russell Henley plays a shot during the final round of the Honda Classic golf tournament in Palm Beach Gardens, Florida on Sunday (US time). Photo: AFP

Russell Henley won the US PGA Tour Honda Classic in Palm Beach Gardens, ­Florida on Sunday (US time) with a birdie at the first hole of a four-way playoff, denying Rory McIlroy in a tournament he'd led for three rounds.

Henley rolled in his birdie putt at the par-five 18th for the victory ­after Northern Ireland's two-time major champion McIlroy, Scotland's ­Russell Knox and American Ryan Palmer had all parred the par-five that served as the decider.

Henley had parred his final three holes ­after a double-bogey at the par-three 15th to close out a two-over-par 72 and finish the tournament on eight-­under 272.

McIlroy endured a difficult day at PGA National, posting a four-over 74, while Knox carded a one-over 71 and Palmer posted a one-under 69.

Despite his struggles, McIlroy had a chance to win at the ­final hole of regulation, where he stuck his 240-yard (219 ­meters) second shot 11 feet (3.35 meters) from the pin, but his eagle putt trickled past.

"Seventy-four wasn't good enough today to get the job done," a stunned-looking McIlroy told reporters.

"Even if I had won it would have felt a little bit undeserved. If I had won today, I would have counted myself very lucky."

In the playoff, Henley was the only player to reach the green in two, and he two-putted from some 40 feet for birdie.

Palmer missed a 10-foot birdie attempt, while McIlroy fired out of a bunker to the front fringe and had to scramble for par and Knox missed a 20-foot birdie putt.

"This isn't going to sink in for a while," said Henley, whose bid for a second career title ­appeared to be over after his double-bogey five at the par-three 15th.

"I don't know what's going on right now. I'm so nervous coming down the stretch, just trying to hang in there, trying to enjoy it."

American Billy Hurley ­carded a 68 to finish fifth on 273. Canada's David Hearn with a 67 and American Will MacKenzie with a 70 shared sixth on 274.

World No.1 Tiger Woods withdrew after 13 holes citing back pain.

Woods, who had barely made the cut but came alive with a five-under 65 on Saturday, was five over for the day when he called it quits.

The 14-time major champion said he didn't yet know if he would be fit enough to defend his title at the World Golf Championships-Cadillac Championship which will be held at the Trump National Doral Miami in Doral, Florida from Thursday to Sunday.

"It's too early to tell," Woods said. "I need treatment every day until Thursday to try to calm it down. We'll see how it is."