DiMarco moved to 20-under-par with Scott Hoch (69), Bob Burns (67) and Skip Kendall (66) all at 18 under.

Joel Edwards (67) is at 17-under-par with Tim Herron (67) and Japan's Hidemichi Tanaka (70) one shot further adrift.

World number one Tiger Woods carded a five-under 67 and is at 14-under-par, tied for 13th.

DiMarco, eyeing his first win since winning January's Phoenix Open, took a combined 44 putts in the first two rounds but totalled 31 on Saturday.

"I think I came out a little more tentative today," said DiMarco, who made just three birdies.

"I don't know why. After shooting 63-64, I think I should have come out more aggressive."

DiMarco was briefly overhauled in the lead by Kendall, who birdied the par-four 13th to reach 20-under.

But Kendall bogeyed two of the final four holes to drop back.

Woods is seeking his third win in this event, but knows he has a lot of ground to make up.

"You need to shoot at least 65 to try to keep pace or move up the board," Woods said.

"If you shoot 68, you're probably going to stay your ground, if not get passed.

"You need to try to shoot three-under par. Right now, par is about 68."