American Roberto Castro coped best with tough, US Open-like conditions at Congressional Country Club as he moved into a two-shot lead after Thursday's opening round of the AT&T National in Bethesda, Maryland.

Seeking his first victory on the PGA Tour, Castro limited the damage always lurking on a course flanked by thick rough and reeled off three consecutive birdies in his last five holes to take control with a five-under-par 66.

Fellow Americans Billy Horschel and Bud Cauley, and Canadian Graham DeLaet, returned 68s while Masters champion Adam Scott of Australia, the highest-ranked player in the field, struggled on the greens on the way to a 73.

"The rough's brutal," Castro told reporters after surging to the top of the leaderboard with a total of six birdies and one bogey. "We probably were 50 percent you'd get it up to the green and 50 percent pitching out.

"It's very similar in that there are not a lot of birdies out there," the 28-year-old said, referring to the US Open feel at Congressional. "You're just plugging along."

Castro, whose best PGA Tour finish was a seventh placing at last year's Greenbrier Classic, totalled only 23 putts on Thursday but had to scramble on several holes to salvage par.

Horschel, who 11 days ago recorded his best-ever finish at a major with a tie for fourth in the U.S. Open at brutally difficult Merion, felt conditions were almost as tricky at Congressional on Thursday.

"It's like another US Open," Horschel said after mixing four birdies with a bogey. "Off the fairways, the rough is thick. It's tough to hit the ball on the green.

"Fortunately, the greens are soft so they're really receptive. But it's still a tough golf course. You've got to drive the ball really well here to give yourself opportunities.

"The tougher the golf course, the better I play," added Horschel, who has posted seven top-10s in 16 starts on the 2013 PGA Tour, including a maiden victory at the Zurich Classic of New Orleans in April.

American world number eight Brandt Snedeker and compatriot Jim Furyk, a 16-times winner on the U.S. circuit, were among a group of eight players who opened with 69s.

Former Masters champions Angel Cabrera of Argentina and Fijian Vijay Singh, and emerging Australian talent Jason Day, started out with matching 70s.

Two notable absentees from Congressional this week are defending champion Tiger Woods, whose foundation benefits from this event, and US Open winner Justin Rose.

World number one Woods pulled out on the advice of his doctors to rest a left elbow strain while third-ranked Englishman Rose opted out due to fatigue since he clinched his first major victory at the Merion US Open.