DORAL, Florida (REUTERS) - American Patrick Reed became the youngest winner of a World Golf Championship event when he held on for a one-shot victory at the Cadillac Championship on Sunday, after an ailing Tiger Woods failed to mount a challenge.

Reed shot a final round of even-par 72 to finish the US$9 million (S$11.4 million) tournament at four-under 284, one shot clear of Bubba Watson and Jamie Donaldson. It was the 23-year-old's third PGA Tour title in eight months.

"I was hitting the ball so good this week and my putting was just outstanding," said Reed. "Whenever you come to an event and feel very confident with your putting, a lot of pressure on your full swing comes off your shoulders," said Reed, who replaces Woods as the youngest WGC winner.

He began the final day with a two-stroke lead and quickly built up a commanding four-shot cushion before fighting off a late challenge from Donaldson.

The Briton birdied the 17th hole to close within one shot of Reed. But when Donaldson bogeyed the last after finding a greenside bunker with his approach shot, Reed was able to lay up and seal victory with a bogey.

Donaldson (68) and Watson (70) finished tied for second at three-under but no-one else finished the tournament under par.

Woods had moved into contention on Saturday with a third round 66 to start the final day three shots behind but returned a six-over 78 to finish tied for 25th.

The world number one did not make a birdie and walked gingerly off the course on Sunday with his health once again a concern ahead of next month's Masters.