Rory McIlroy and Padraig Harrington inched up the leaderboard on day three of the Valero Texas Open, but it was Billy Horschel who continued to head the field.
After successive 68s on Thursday and Friday, Horschel - second at last week's Shell Houston Open and seeking his first PGA Tour win - shot 70 to retain a two shot advantage at the summit.
Two more Americans, Jim Furyk and Charley Hoffman, shared second place following respective rounds of 69 and 70.
Then came McIlroy, one of three players tied for fourth on six under after a 71 that saw three bogeys sandwiched by four birdies.
Alongside McIlroy were Ryan Palmer, whose 68 represented the round of the day, and Bob Estes, the winner of this event 19 years ago.
Harrington was a further shot back, along with Scotland's Martin Laird, while Germany's Marcel Siem reached four under courtesy of a 69.