The Northern Irishman was in a three-way tie for the lead heading into the final round at Riviera but a two-over 73 saw him finish on eight under par.

Scott carded a one-under-par 70 to win by two strokes from South Korea's Sung-hoon Kang and Americans Matt Kuchar and Scott Brown.

Tiger Woods finished 22 shots back, last among those who made the cut.

"It's a very special win this week," said former world number one Scott, 39. "They're not coming easy for me these days so I'm going to savour this one.

"It's a great way to start [2020]. This has to be my year. I can't afford to let the next 10 years slip away. I have to make it happen now."

Victory marked Scott's first PGA Tour title since 2016 but he had to overcome a double bogey six on the par-four fifth, the same hole on which McIlroy hit a triple bogey.

He followed that with three birdies, all but sealing the win with one from 10 feet on the penultimate hole, before parring the last to finish on 11 under.

But McIlroy never recovered from his slip-up, bogeying two further holes to finish tied for fifth.

"Definitely the toughest day of the week," said the 30-year-old world number one.

"The wind was up, hole locations were sort of tricky spots, the course was firming up again. Everyone was finding it tough out there."