Roberto Castro: His only dropped shot on Thursday came when he found water at the 11th
An opening 66 proved enough for Roberto Castro to hold a two-shot lead at the end of the first round of the AT&T National.
The American produced a run of three straight birdies on his back nine; his only dropped shot of the day came at the 11th - his second - when he found water with his approach, though he saved bogey thanks to an excellent chip.
First round leaderboard
(US unless stated)
-5 R Castro
-3 B Horschel
-3 B Cauley
-3 G DeLaet (Can)
Click here for collated scoresnn
Castro finds himself ahead of compatriots Billy Horschel and Bud Cauley and Canadian Graham DeLaet on a day when low scores were at a premium.
Despite the relatively soft conditions and the mild weather in Maryland, the thick rough and course length made life far from easy for the field at the Congressional Country Club.
Horschel - who began his day with a 50-foot birdie putt as he picked up three shots in his opening four holes - was the early leader after a score of 68, though he admitted afterwards he had found it hard work.
"It's like another U.S. Open," Horschel - who tied for fourth in the second major of the year at Merion - said.
"Off the fairways, the rough is thick. Fortunately, the greens are soft so they're really receptive. It's still a tough golf course."
Nicolas Colsaerts is the leading European after finishing up in an eight-man group at two under, the Belgian mixing three birdies with as many bogeys on a see-saw front nine before coming back in a blemish-free 34 shots.
Fabian Gomez of Argentina also signed for a 69, along with Americans Jim Furyk, Ben Kohles, Russell Henley, Brandt Snedeker Jordan Spaith and James Driscoll.
Englishman Brian Davis is a further shot back on one under, the same total as Australian Jason Day and Vijay Singh of Fiji.
Some, though, found the going much tougher - Davis Love III withdrew with a sore hip after an 83, while Rory Sabbatini called it quits when eight over after 12 holes due to a back injury.
Reigning champion Tiger Woods is unable to defend his title this week due to an elbow injury that will keep him out of action until the Open.