Kirk Triplett is alone in second place at 6-under-par 64, while Davis Love III and Jason Bohn are knotted in third place at minus-5. Matt Gogel and Tom Pernice, Jr. share fifth at 4-under-par 66.
Leonard wasted little time in breaking into red figures on Thursday. He birdied his first three holes, all from inside 5 feet, then added another at the fifth when his 7-iron stopped 15 feet from the hole.
At the seventh, Leonard hit another 7-iron, but the ball came to rest almost 60 feet from the cup. He drained the long birdie putt and birdied the ninth to make the turn in 29.
'It is hard to feel a 29 coming,' admitted Leonard. 'But, I felt pretty good the last couple of days.'
Leonard had some trouble on the back nine. At the 13th, Leonard ran home a 6-foot par save, then one hole later, sank a 10-footer to save par and keep his bogey-free round intact.
The Texan rebounded at the next hole when he hit a sandwedge to 5 feet. Leonard collected his eighth and final birdie at the 17th when he knocked a 9-iron to 20 feet.
'Yesterday in the Pro-Am, everything got better as the day went on,' said Leonard, who won the 1997 British Open. 'By the end of day I was hitting the ball pretty well.'
Leonard is in the middle of a long stretch of golf. He has played the last three weeks after taking a month off for the birth of his second daughter. Leonard won the Bob Hope earlier in the season, but has only one top-15 finish and three missed cuts since.
On Thursday, he felt like the round, which featured 16 of 18 greens in regulation, was a long time coming.
'I feel like I played my way into this round,' said Leonard. 'Certainly shooting 62 is a surprise. I felt like that coming into this week I was in a pretty decent place. After the last two days working, everything felt pretty good.'
Triplett started on the back nine Thursday and birdied the 12th from 15 feet. He recorded his second birdie of the round at 17 when his 7-iron approach landed 18 feet from the cup. Triplett made it back-to-back birdies at 18 after a 5-iron came to rest 10 feet from the hole.
Triplett collected his third birdie in a row at the first and added another at the par-5 third. He laid up and knocked his approach to 8 feet. At the fifth, Triplett drove into the trees, but managed to get his approach under the branches through the green. He made par, then rolled in an 18-foot birdie putt at seven to get within two of Leonard.
'The pins were for the most part set up so you could get at them, bouncing the ball in,' said Triplett. 'There was a couple you needed to stay away from. That shows on the scoreboard a little bit. Some of the guys with some experience were playing it out there 20, 30 feet.'
Bob Estes, the 2001 champion, Olin Browne, Paul Goydos, Hank Kuehne, Hunter Haas, Scott Gutschewski, Will MacKenzie, Phillip Price, Carl Pettersson, Roland Thatcher and Lucas Glover are tied for seventh place at 3-under-par 67.
Kenny Perry, who won last week's Colonial, struggled a 3-over 73 and is tied for 101st place.