Heath Slocum used a 67 to move into second place at 9-under-par 201 while Tom Pernice, Jr. took third place at 8-under-par 202. Davis Love III, Fred Funk and Paul Goydos share fourth place at 7-under-par 203.
The 32-year-old played his second shot to the back fringe at the par-4 ninth and two-putted for a par. Leonard then dropped his approach inside 12 feet at the par-4 10th, but was unable to convert the birdie try.
At the par-3 11th, Leonard landed his tee shot to the right of the hole and watched as his ball rolled within inches of the cup. He tapped in for a birdie and continued to run off pars on the back nine.
'The wind is so light here that it kind of changes a little bit here and there,' Leonard said of his shot on the 11th. 'When I hit it, the wind was into me a little bit.'
Leonard rolled in a 12-foot putt for a birdie at the par-5 16th and parred his two remaining holes to secure the largest 54-hole lead of the 2005 season on the PGA Tour.
'It is nice to have the lead, certainly a lead this big,' said Leonard, who hoisted the claret jug in 1997. 'I certainly am playing in a nice rhythm right now and playing with confidence.'
Slocum birdied each of his first two holes, but he gave a shot back with a bogey at the fourth. He countered with back-to-back birdies from the sixth to reach 9 under, but found trouble again with a bogey at the eighth.
The 31-year-old got back to minus-9 with a birdie at the 11th, but again he followed up with a bogey at the 12th. Slocum then sank a 10-foot birdie putt at the 16th finish alone in second place.
'It is hard to expect anything less than him playing a good solid round,' Slocum said of the prospects of catching Leonard on Sunday. 'All I can do tomorrow is go out and play the golf course the only way I can play it. I am not going to change strategy or anything. Hopefully I will hit it well enough tomorrow to give myself some chances.'
Pernice had two birdies and a bogey over his first nine holes. A birdie at the 11th lifted him to 8 under and he ran home a long birdie putt at the par-3 14th to move to minus-9. Pernice stumbled down the stretch with a bogey at the 17th, however, and parred the last for a round of 68.
Defending champion David Toms, who had a seven-shot lead heading into the final round of this event last year, fired a 65 to move into a tie for seventh place. He was joined by Fredrik Jacobson, Bob Estes, Richard S. Johnson and Phillip Price at 6-under-par 204.
Billy Andrade, Roland Thatcher and Mathias Gronberg finished knotted at 5- under-par 205.