Billy Horschel carded a 4-under 68 on Friday to grab a 2-stroke lead at the Valero Texas Open.
Horschel, who is seeking his first career win on the PGA Tour, finished 36 holes at TPC San Antonio at 8-under-par 136.
Charley Hoffman fired a 5-under 67 during his second round to move into a share of second place. He is joined by Daniel Summerhays (69) and Steven Bowditch (69) at 6-under.
Two-time major champion Rory McIlroy carded a 5-under 67 to move into a group of seven players tied for fifth place at 5-under-par 139, which also includes 16-time PGA champion Jim Furyk (70).
"I definitely feel like I made the right decision to come here, and even if I hadn't been in this position and have been a few shots back, I'd still feel the same way," said McIlroy, who added this event to his schedule at the last minute to better prepare for The Masters next week. "I haven't really been in contention this year, so it will be nice to get into the mix."
Horschel entered the day a shot behind first-round co-leaders Matt Bettencourt and Peter Tomasulo, but quickly fell further off the pace as he opened with a bogey at the first and then followed a pair of pars with another 2-putt bogey at the fourth.
He would not drop a shot for the rest of the day, however, and righted himself with a string of three straight birdies from the fifth, including a 15-foot putt at the sixth.
He then parred the next six holes before rolling in another birdie effort from just beyond six feet at the 14th to tie clubhouse leaders Hoffman, Bowditch and Summerhays.
Horschel pulled ahead with an 11-foot birdie putt at the 17th, and closed with another 11-footer at the last to gain some breathing room entering the weekend.
"I think if I keep doing what I'm doing everything will fall into place," Horschel said. "It felt pretty good out there today and we'll see how it goes tomorrow."
Hoffman quickly started to make his move on the day as he opened his round with three straight birdie putts from inside 10 feet starting at the first.
After parring the next 10 holes, he moved to 4-under for the tournament with an 8-foot birdie putt at the 14th.
He stumbled to a 2-putt bogey at the 15th, but he got that stroke back plus another as he closed his round with a pair of 8-foot birdie putts at the 17th and 18th to move into a share of the lead.
"It was fun. I started off really well with three birdies and I actually played the rest of the round pretty good," said Hoffman. "I just didn't make any putts and then I made a couple coming in and it all led up to 5-under, and a 5-under around this place is always pretty good."
Summerhays and Bowditch both countered three pars with six birdies during their second rounds to move into contention.
NOTES: Horschel extended his consecutive cuts-made streak to 21 events ... Bettencourt and Tomasulo each carded a 1-over 73 on Friday and sit among a group tied for 12th place at 4-under-par 140 ... Bill Lunde withdrew during his second round ... The cut line was set at 1-over-par 145, with 82 players advancing to the weekend ... 2012 champion Ben Curtis carded a 1-under 71 during his second round to just make the cut on the number.