Overnight joint leader Andrew Landry dropped three shots on the back nine but finished with two birdies to take The American Express title in California.
Landry was in the box seat at La Quinta, reaching six under for the round after the 12th.
But three straight bogeys opened the door to the chasing pack until the American slammed it shut by picking up shots on the par-three 17th and par-four 18th, a 67 bringing him to 26 under for the tournament and his second PGA Tour win.
Mexican Abraham Ancer had played himself into contention with a nine-under round of 63 but had to settle for second place, while Landry's fellow leader after Saturday, Scottie Scheffler, mixed three birdies with three bogeys on the front nine and finished up third a shot further behind.
Paul Casey was the best of the British contingent with his final round of 71 seeing the Englishman fall 12 places down the leaderboard into a tie for 21st.
Scotland's Russell Knox carded a 68 to move up 19 places into a tie for 37th.