By John Reger
Joint overnight leader Johnson's wayward two-over 74 was enough to see off late challenges from fellow Americans David Duval and J.B. Holmes and made him the first back-to-back winner at Pebble Beach since Mark O'Meara in 1989-90.
"I certainly try and win every week I am out here. I'm playing well right now," the 25-year-old said after picking up a $1.12 million winner's cheque.
Johnson, who won by default last year after leading when the fourth round was washed out, started the day with a shared four-stroke lead with American Paul Goydos, but opened his round with a bogey.
After recovering with an eagle on the sixth to regain the lead, the American slipped again on the ninth with a double-bogey and another dropped shot on the 12th.
Goydos crashed out of contention on the back nine with a horror five-hole stretch of three bogeys and a quadruple-bogey nine on the par-five 14th, but Duval and Holmes made late charges to pressure Johnson.
Former world number one Duval, who started the day six adrift, stormed back into contention with a 12-foot birdie putt on the par-three 17th, after Holmes birdied the 16th.
Under pressure, Johnson bogeyed the 17th to fall back into a three-way tie with Duval and Holmes going into the last hole.
Duval's wedge shot from 105 yards on the par-five 18th spun back to the front of the green and the American was unable to hole the 27-foot birdie putt.
Holmes then missed a 13-foot birdie putt to put the tournament in Johnson's hands.
The big-hitting American, whose tournament campaign had been built on attacking the three courses' par-five greens, threw caution to the wind. After splitting the fairway, he went for the green in two, but instead found a green-side bunker on the right.
Having made only two of seven sand saves in the tournament, Johnson's wedge shot barely cleared the lip, but settled four feet from the pin.
"It was a long day," Johnson said. "I had a short putt which is what you want to win a tournament."
(Editing by Ian Ransom)