Len Mattiace fired a closing 68 at the $3.7 million Nissan Open on Sunday to claim his first US PGA Tour victory at the 220th attempt.
Mattiace finished 15-under-par on 269, one stroke better than McCarron, Brad Faxon (68) and South African Rory Sabbatini (68).
Mattiace (34) parred the 18th while overnight leader Scott McCarron, who led most of the day, bogeyed the last hole.
McCarron, who carded a level-par 71, was one stroke ahead of the eventual winner on the 17th tee. But Mattiace birdied the 17th while McCarron could only manage a par, setting the stage for their thrilling finale at the 18th.
Mattiace has never finished higher than 61st on the money list in seven years on the tour. He arrived at the Riviera Country Club ranked 157th in the world.