Jimmy Walker held his nerve to win the AT&T Pebble Beach National Pro-Am by a single shot, his third win of the PGA Tour season.

Having seen a six-shot lead gradually eroded on the final day, Walker three-putted the 17th and, needing a closing par, missed the fairway and chased his first putt five feet past the hole.

He needed to hole the one coming back the other way if he was to avoid a play-off with Dustin Johnson and Jim Renner and, though the ball threatened to dive left, it dropped to secure a nervy win.

Graeme McDowell shot an impressive final round 67 o move into a tie for seventh place, five shots off the lead.

Padraig Harrington finished with a level par round of 72 to finish in a share of 27th on two under.

"It was good TV, wasn't it?" Walker quipped on Sky Sports 4.

The win followed Walker's previous successes at the Sony Open in Hawaii and the Frys.com Open in California.

Rounds of 66, 69 and 67 had taken him to 13 under ahead of the final round, with Hunter Mahan his nearest challenger at seven under.

The latter was unable to improve on that score as a wayward finish left him to settle for a closing 72, meaning the challenge came from Mahan's Ryder Cup colleague Johnson and Renner.

Renner began the day five under and birdied five of the back nine to move into contention, while Johnson went one better with a six-under-par round of 66.

A delicate chip-in saw him eagle the second hole and he played the front nine in three under as a good putt at the ninth earned him a second straight birdie.

A stone-dead approach at 15 and a solid putt at 16 put him in contention but he left an ultimately crucial eagle putt short at the last, settling for birdie and 10 under for the week.

"It was not a good effort," he said of that eagle putt. "But the greens are tough and if you've got 30-footers, it's tough to get a good roll."

Rising star Jordan Spieth was eight under alongside fellow American Kevin Na, with Mahan on his own at seven under. Pat Perez and Tim Wilkinson finished on six under.