Roberto Castro shot 5-under-par 66 on Thursday and grabbed a 2-stroke lead through one round of the AT&T National.
Castro, who turned 28 on Sunday, tallied six birdies against just one bogey and carded an opening-round 66 or better for the fourth time this season. He is seeking his first career PGA Tour win in his 48th start.
Billy Horschel, who tied for fourth at the U.S. Open, sits two shots off Castro's pace at 3-under 68. He is joined there by Bud Cauley and Graham DeLaet.
"It's like another U.S. Open," Horschel said of the conditions at Congressional Country Club's Blue Course. "Off the fairways, the rough is thick. Tough to hit the ball on the green.
"Fortunately, the greens are soft, so they're really receptive. It's still a tough golf course. Got to drive the ball really well here, give yourself opportunities."
World No. 8 Brandt Snedeker, Jim Furyk and Nicolas Colsaerts are among a group of eight players tied for fifth place at 2-under 69, while Jason Day and Angel Cabrera sit alongside 13 others at minus-1.
"It's just a long, hard golf course," said Furyk. "I'm hitting a lot of long irons."
Tournament host Tiger Woods is not on hand to defend his 2012 title due to an elbow injury.
Castro, whose best finish on tour this season is a tie for 16th at the Waste Management Phoenix Open, began Thursday's round on No. 10 and parred that hole before tripping to a bogey at the 11th. He rebounded with back-to-back birdies from the 12th, then tallied five straight pars to reach the turn at 1-under.
"The rough's brutal," he said. "We probably were 50 percent you'd get it up to the green and 50 percent pitching out."
Around the turn, Castro added another gain at the first, then notched a trio of pars before taking the lead with a hat trick of birdies from the fifth. He parred his final two holes to close with the 2-stroke advantage.
"If I play a good round and I play well, I can play as good as anybody," continued Castro, who had 23 total putts and didn't miss from inside 10 feet on his round.
NOTES: Castro carded his best round since shooting 63 in the first round of the Players Championship in May. He shot 78 in the second round of that event ... Masters champion Adam Scott, ranked fourth in the world, carded an opening-round 73. He hit 15 greens, but took 35 putts ... U.S. Open champion Justin Rose pulled out of this tournament due to fatigue.