Four strokes off the pace going into the final round, the American left-hander seized control with five birdies in the first eight holes on the way to a flawless seven-under-par 64 at a sun-splashed Riviera Country Club.
Watson, who has long relished playing at the revered venue despite never having posted a top-10 finish in seven previous starts, capped his round in style, rolling in a 14-foot birdie putt at the last to post a 15-under total of 269.
"I am hitting the ball really well ... and it worked out this week," an elated Watson told CBS Sports after clinching his fifth PGA Tour title and the winner's cheque for $1.206 million.
"Things are great right now," said the American, who went bogey-free at Riviera over the weekend as he fired successive 64s.
Watson's final round was the lowest by a champion at Riviera since Doug Tewell's 63 in 1986 sealed a seven-shot victory.
He came into the tournament having recorded two top-10s in his first four starts on the 2013-14 PGA Tour, his best finish a tie for second at the Phoenix Open earlier this month.
"Today, I got hot early, holed a bunker shot on six to really get it going and went bogey-free in the last round," said Watson.
"I was looking at: 'There's a number out there and I'm going to shoot it. I have to shoot it and I have to go out there and play good golf'.
"You're always looking at trying to beat the golf course first, so that was my goal," said the American, who was embraced after the round by his wife Angie and their son Caleb, who will celebrate his second birthday in two weeks' time.
Long-hitting American Dustin Johnson, one of four players who held at least a share of the lead during Sunday's final round at Riviera, closed with a five-birdie 66 to finish alone in second.
Monday qualifier Jason Allred and fellow American Brian Harman signed off with 68s to share third place at 12-under, a stroke better than 2011 Masters champion Charl Schwartzel of South Africa, who also carded a 68.
American journeyman William McGirt, bidding for his first PGA Tour victory, began the last day with a two-shot lead but slid back with a 73 to finish five strokes behind Watson.
McGirt had maintained his overnight advantage with a comfortable two-putt birdie at the par-five first, the easiest hole on the course.
However, he stumbled with a bogey at the tricky par-four second, where his approach ended up just short of the green before he ran his first putt nine feet past the hole.
On a course running fast and firm under a dazzling sun, several of McGirt's closest pursuers began to pile on the heat and, for a while, four players were tied at the top at 12-under: McGirt, Watson, Harman and Schwartzel.
Watson, who had holed out from a greenside bunker to birdie the sixth, broke the deadlock by draining a 16-footer to birdie the par-four eighth before reaching the turn in a blistering five-under 30.
The American left-hander, who made the cut by just two shots after scores of 70 and 71 before charging up the leaderboard with a sizzling 64 in the third round, then forged two strokes clear with a birdie at the par-five 11th.
Watson did well to par the treacherous 12th, where he sank an eight-foot putt, before Johnson trimmed his lead to just one with a birdie at the 15th.
Watson refused to buckle and held on to secure victory with pars on the next five holes before collecting his seventh birdie of the day at the par-four 18th.
"He must be hitting the ball great and be in great control of his golf ball because the golf course, the greens, are really firm," Schwartzel said of Watson's performance. "It's difficult. You need to hit good shots here."