A stroke in front of the chasing pack overnight, Tour veteran Mediate fired a sparkling six-under-par 65 for a 13-under total of 129 at CordeValle Golf Club.
The 47-year-old American needed a total of only 23 putts as he ended a sunny day three ahead of Japan’s Ryuji Imada, who carded a 67.
Former world number one David Duval fired a bogey-free 65 to lie four shots off the pace, level with fellow American Dean Wilson (64).
U.S. Ryder Cup player Rickie Fowler (65) and Swede Henrik Stenson (67) were among a group of five bunched at eight under in the third of five events in the PGA Tour’s Fall Series.
Mediate, who won the most recent of his five Tour titles at the 2002 Greater Greensboro Classic, was delighted to be in a good position to end his victory drought on the U.S. circuit.
“I want it,” he told reporters. “I want to be able to go out tomorrow and see what I got. I like to have attention, but I just want to see what I can do out there. I can’t wait.”
Having opened with a blistering 64 that included a hole-in-one, Mediate experienced a measure of self-imposed pressure overnight in his bid to maintain form.
“Starting out this morning, I was a bit nervy for sure because you just want to go out and try to shoot (a good number),” he said. “Did I think I was going to shoot six or seven under? No.
“You never think that’s going to happen, but, of course, I want it to. The human factor kicked in a little bit. But it was good. My game was solid all day.”
Mediate drained a monster 40-foot putt at the par-five 12th for – m his first birdie of the day after playing the back nine first.
Out in three-under 33, he conjured another magical shot when he holed out with a seven-iron from 158 yards to eagle the par-four fourth.
“I hit it a foot or two to the right of the pin, there is a slope out there and it kicked up a little bit,” Mediate said.
“One of the marshals was standing by the ropes and he is walking it down going: ‘Go, go, go’. It was pretty cool.”
The cut fell at level-par 142 with former major winners Trevor Immelman of South Africa and Americans Mark Brooks and Tom Lehman among those missing out.