Bubba Watson holed a bunker shot at the 14th hole to set the stage for a two-stroke triumph at the Genesis Open - and 10th PGA Tour title - in Los Angeles, as Graeme McDowell's challenge completely fizzled out.

McDowell was still in the hunt going into the final round following his one-under 70 on Saturday that left him just two shots behind Watson on eight-under-par.

However, the Northern Irishman slumped to a six-over 77 to sign off on two-under for the tournament.

He started perfectly with a birdie on the first but didn't manage another and bogeyed seven holes, include six of seven between 9 and 15. 

Watson pulled away with another birdie at the par-five 17th, shooting a closing two-under-par 69 at Riviera.

The long-hitting left-hander finished at 12-under 272 for his third victory at Riviera, after previous successes in 2014 and 2016.

It was a moment to savour at the Riviera Country Club in Pacific Palisades, Los Angeles, for Watson, 39, who had considered retiring due to concerns over his physical ability.

Overcome with emotion, he told CBS: "It means a lot, my goal was always to get 10 wins and this got me to my 10th win. There's so many emotions going around my head right now. You never know if you're going to play good again, you never know if you're going to be able to lift a trophy again."

After his 10th PGA Tour open win, the third at the Riviera, Watson paid tribute to his family and caddie Ted Scott.

"I've mentioned it (retirement) about 10, 12 times to my wife, we've sat down and had may talks about it because physically I wasn't where I needed to be to keep continuing to play," he said.

"Obviously God's given me a gift to play golf and I'm not good at anything else."

Ben Hogan and Arnold Palmer also won the event, previously known as the Los Angeles Open, three times each.

Fellow Americans Kevin Na and Tony Finau tied for second on 10-under.

A two-times Masters champion, Watson will jump back into the top-50 in the world after starting the week ranked 117th.

Rory McIlroy put in a strong final round to finish a stroke better than McDowell.

The four-time major winner ended his tournament with a 68 to follow rounds of 71, 69 and 73 to finish on three-under.

The 28-year-old has now gone 16 months without winning a tournament but his performance at the Riviera Country Club was an improvement on the previous week when he missed the cut at the AT&T Pebble Beach Pro-Am.

Padraig Harrington ended on five over after a disappointing 74 in which he hit two birdies and six bogeys.