Rookie Jeff Overton and veteran Tom Pernice Junior share the lead at the halfway stage of the AT&T National at the Congressional Country Club, Bethesda, Maryland.
The pair are on nine-under-par after the first two rounds, three shots ahead of Anthony Kim and Cliffe Kresge, while Australian Rod Pampling heads a group of seven players one shot further adrift.
Overton had been in second place overnight and added a round of five-under to move to the top of the leaderboard.
The 25-year-old carded a mistake-free round, picking up two birdies on the front nine and three more towards the end of the day.
Pernice joined Overton after carding the round of the day, a 63, which propelled him up the leaderboard from 13th at the start of the day.
The 48-year-old only dropped one shot all day and made eight birdies, including a run of four consecutive ones between the sixth and ninth, to put him ahead of the field.
Pernice said he was pleased to have achieved the round on such a difficult course as the one at the Congressional Country Club.
He said: "I've been playing well and you never know when a round like this is going to jump up. I'm thrilled at my position.
"Shooting a 63, seven-under-par around this golf course is pretty special."
Kim remains in contention after carding his second successive round of 63, while two bogeys on the back nine cost Pampling the chance to join Overton and Pernice at the top of the leaderboard.