Australian Stuart Appleby took a major step toward capturing his first title of the year by shooting a two-under-par 68 to move two strokes clear of the field on a steamy Saturday at Congressional Country Club.
The 36-year-old, bidding for his ninth career title, stands at nine-under 201 for the tournament.
"If I can go out and play as well as I have been playing and think and relax and just play, I think I can squeeze a couple more birdies out tomorrow," said Appleby.
"It's just hard to shoot six under par around here, it really is. Today, with the way the course is, and even tomorrow, it's going to be hotter.
"It's going to be in the high 90s. It's going to be even harder."
South Korean K.J. Choi, who opened the day tied with Appleby, sits in second after shooting an even-par 70. American Steve Stricker is in third, a stroke behind Choi after firing a 67.
World number one Tiger Woods, doubling up this week as player and tournament host, failed to make a serious run at the leaders by shooting a one-under 69.
The new father is two-under for the tournament and in a tie with Jim Furyk and Kevin Stadler for eighth place, seven strokes behind Appleby.
Choi trailed Appleby by five after shooting a bogey on the par-four 14th but rallied with birdies on the next three holes to move back into contention for his sixth career title.
"Putting was really difficult today," Choi said through an interpreter. "It was very hard to grasp the speed of the greens. It made the front nine very difficult.
"But luckily on the back nine, I was able to come back nicely on the next three holes and finished out pretty good."
Woods opened Saturday's round with a birdie but failed to record another until the par-five 16th. The 31-year-old American gave it back on the 18th, however, when a 10-foot putt drifted wide for a bogey.
Despite being well down the leaderboard, Woods said he was not going to go out quietly during Sunday's final round.
"I've got to make a run and then see what happens behind me," he said. "And I have to handle my own business first before anything can happen."
Canadian Mike Weir was in fourth place, four shots off the pace, while American Lucas Glover was placed fifth, a shot adrift of Weir after firing a 66 on Saturday.
The day's best score was turned in by Japan's Shigeki Maruyama, who carded a five-under 65 to jump in a tie for sixth place with a three-under 207 after 54 holes.