Padraig Harrington produced a sizzling four-under-par 68 to lie four shots off the lead at the Texas Open.

Harrington, chasing a his first victory in over a year in San Antonio, carded seven birdies to give himself a chance heading into the final round.

American Ricky Barnes, a former US amateur champion seeking his first PGA Tour victory, birdied four of the last eight holes to grab a one-shot lead.

Though he bogeyed the par-five 18th after pulling his tee shot left into tall grass, Barnes delivered a superb exhibition of pinpoint approach play for most of the day as he fired a five-under-par 67 on the Oaks layout at TPC San Antonio.

Playing his eighth full-time season on the PGA Tour, Barnes posted an 11-under total of 205 to end the round a stroke in front of his compatriot Brendan Steele, the 36-hole leader who slipped off the pace as he ground out a 72.

American Charley Hoffman, bidding for his fourth win on the US circuit, carded an adventurous 70 on a sun-splashed afternoon to finish at nine-under, level with England's Luke Donald (68).