Jason Day and Marc Leishman made strong starts to the AT&T National as both stayed in touch with leader Bo Van Pelt on Thursday (local time).
American Van Pelt produced a bogey-free round at the Congressional Country Club, holing two birdies and an eagle to hold a one-shot lead after a four-under 67.
Fijian Vijay Singh, Zimbabwean Brendon de Jonge and American Jimmy Walker are tied for second at three under after just 22 players finished under par.
Tiger Woods, winner of the PGA Tour event when it was last held at Congressional, was not among them after carding a one-over 72.
Day, who has struggled this season, managed a two-under 69 after a rollercoaster round, which included six birdies and four bogeys.
Leishman, fresh from his win at the Travelers Championship, continued his good form with a one-under 70.
Fellow Australians Rod Pampling (even par) and Greg Chalmers (one over) were also solid.
But Adam Scott, the highest-ranked Australian in the world, struggled, finishing at four over alongside countryman Robert Allenby.
Nick O'Hern (11 over) is all but certain to miss the cut after an opening round littered with bogeys and double bogeys.
Just a year after the US Open field found scoring easy at the course, tougher pin placements and a heat wave have made life harder for the players.
Van Pelt, who holed out from 93 yards for an eagle on the first hole, said he expected scoring to be tough throughout the tournament.
"It's all you want out there right now," he said.
"Basically you could have a US Open here this week if you wanted it. The rough is very uniform, it's very thick.
"The greens are firm and they're fast. It's a great golf course, and when it's set up like this, it's going to play tough all week."
Singh's inconsistent round included seven birdies and four bogeys, while de Jonge and Walker rued bogeying the par-four 18th hole.
American pair Billy Hurley III and Pat Perez and Australian Jason Day are tied for fifth at two under.
Reigning champion Nick Watney is a further shot back in a group of 15 players including the likes of Dustin Johnson and Hunter Mahan.