"It's like another U.S. Open," Horschel 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."
Congressional has hosted the U.S. Open three times, and it looks like it could handle another with a moment's notice.
The course is among the longest this year. The rough is denser than usual, putting an extra premium on the tee shot.
Jim Furyk, Nicolas Colsaerts and Ben Kohles were at 69, and no one else from the morning managed to break 70.
Lucas Glover, a former U.S. Open champion, called it "the most boring round of PGA Tour golf I've heard."
"I heard two cheers across the whole golf course all morning," Glover said after a hard-earned 71. "They definitely weren't for my group."
U.S. Women's Open
Top-ranked Inbee Park took the early lead in the first round of the U.S. Women's Open in Southampton, N.Y., as she tries to make history by winning the first three majors of the year.
Park had just one bogey in a 5-under 67 for the best score of Thursday's morning groups. Caroline Hedwall of Sweden was a shot back, with six players at 2 under.
John Huston shot a 5-under 65 on Thursday to take the first-round lead in the Senior Players Championship.
Huston started on No. 10 and was even par halfway through his round before making a big move on the front nine at soggy Fox Chapel in Pittsburgh. Huston shot 5-under 30 coming in, including four birdies and an eagle on the short par-4 seventh. The 52-year-old Huston missed three months this season because of lower-back problems.
Roberto Castro -5
Billy Horschel -3
Bud Cauley -3
Graham DeLaet -3
Daniel Summerhays +7