Phil Mickelson kick-started his US PGA golf Tour season by retaining the Northern Trust Open.

The 38-year-old, who came into the final round four shots ahead of the field, saw his advantage reduced to just one stroke.

Mickelson finished on 15-under par after a closing effort of 72 at the Riviera Country Club, leaving him one shot ahead of countryman Steve Stricker on 14-under.

The Callaway Golf star had sunk two behind Stricker with two to play, but birdied the 16th and 17th, while Stricker dropped a shot on the last.

"Standing on the final tee two years ago, I had a one-shot lead but drove it in the rough and made a bogey," explained Mickelson who was runner-up in 2007.

"I stood out there today, hit three-wood, put it in the middle of the fairway, put a six-iron just out on the fringe and was able to two-putt for par. That was important to me."