Loren Roberts carded a 69 to join Peter Lonard in a tie for fourth at 24-under-par 336. John Senden and Tim Herron were one shot further back at 23-under-par 337.
Leonard was three shots behind Ogilvie heading into the final round, but the Texan had all the momentum. Leonard was dealt the Palmer Course at PGA West on Saturday, one of four courses that shared play over the first four rounds. He fired a 64 in the fourth round and picked up where he left in the final round, playing PGA West for the second straight day.
'When you're coming from behind there's not a whole lot of room for error,' said Leonard. 'You have to hit good shots, you have to do those things and play aggressively. Sometimes on a course like this, that may be a little easier.'
The 32-year-old was firing on all cylinders early on with back-to-back birdies from the first to surge into a tie with a struggling Ogilvie. Ogilvie fell one shot back with a bogey at the third, his second dropped shot of the day, and Leonard pulled two strokes clear with a birdie at the par-4 fourth.
Leonard stumbled to a bogey at the par-3 fifth, but got that shot back with a birdie at the par-4 seventh. He then hit his second shot to 10 feet for a birdie at the par-4 10th and followed that up with a birdie at the very next hole to stand four shots clear of the field.
He flew his second shot over the green at the par-4 13th, but got up and down for par. Leonard had a birdie chance at the 16th after his approach landed within 11 feet of the hole but the putt didn't fall.
Leonard continued the par streak down the stretch and the advantage he had built was more than enough to hold for his ninth career victory on the PGA Tour.
'My game just seemed to get a little better every day here,' said Leonard, who won for the first time since the 2003 Honda Classic. 'I got a little more comfortable with the shots I was trying to play and got more comfortable.'
Ogilvie tried to shake his early troubles with a birdie at the par-3 fifth, but PGA West caught up to him on the back side. He sent his tee shot into the water at the par-4 10th and scrambled for a double-bogey.
Ogilvie responded with a birdie at the 11th, but was unable to make a move from that point on. A birdie at the 18th put him in a tie for second with Clark after a round of 73.
'The rain dance didn't work last night,' said Ogilvie. 'I was trying for a rain-out but it didn't happen. I certainly didn't play the way I would have liked today, but I got a pretty good front row seat for a great round of golf.'
Clark, who won the South African Open last week, collected a pair of birdies and a bogey over his first nine holes. He then birdied the 11th but found trouble with a bogey at the 13th.
The 29-year-old birdied two in a row starting at the 14th to reach 25 under, but he fell off the pace again with a bogey at the 16th. Clark then birdied the last to secure a share of second.
Former U.S. Open champion Jim Furyk managed a 71 to share eighth place with Ian Poulter, Jerry Kelly and Andrew Magee at 22-under-par 338.
Phil Mickelson, the winner here in 2002 and 2004, followed at 21-under-par 339 along with Ryuji Imada.