Hunter Mahan surged to the top of the AT&T National leaderboard with a six-under-par 65 which put him two strokes clear of the field at the halfway point in Maryland.
Mahan's round of seven birdies and a bogey on another stifling day at the Congressional course put him seven under overall, two clear of two fellow Americans, Jimmy Walker and Robert Garrigus, as well as Zimbabwe's Brendon de Jonge.
Behind them on four under was a group of five which included Stewart Cink and Vijay Singh, while Tiger Woods carded a much-improved 68 to sit ominously on two under alongside overnight leader Bo Van Pelt.
With temperatures reaching 109 degrees Fahrenheit, Mahan said mastering the conditions was key.
"When the conditions and the weather comes into play, it's a whole other factor," he told the PGA Tour's official website.
"I've got to stay mentally tough. Once your mind goes, the body is going to go with it. It's very important to be mentally strong.
"We've got two more days of this, so it's going to be important to take care of yourself every night and every day when you're out on the golf course, or it's going to cost you shots."
Woods sunk a 48-foot eagle putt on the 16th hole, helping him move into a tie for 11th.
Woods, starting five shots behind overnight leader Van Pelt, went three under par to reach a two-under total of 140.
Woods said: "It's just one of those days where you just stay patient.
"You shoot something in the 60s, and I think that would have been a good score. I thought it was a very good score. I'm right there."
Van Pelt hit a disappointing second round of 73, including six bogeys, while Glasgow's Martin Laird made a move with a fine two-under 69 to sit one under overall.
Defending champion Nick Watney was one behind Laird after going one over.
England's Greg Owen was four over for his round but made the cut on three over, the same mark as Beau Hossler, the 17-year-old amateur who made headlines at the US Open.
Collated second round scores & totals in the USPGA Tour AT&T National, Congressional G & CC, Bethesda, Maryland, United States of America
(USA unless stated, par 71):
135 Hunter Mahan 70 65
137 Brendon De Jonge 68 69, Robert Garrigus 70 67, Jimmy Walker 68 69
138 Vijay Singh (Fij) 68 70, Rodney Pampling (Aus) 71 67, Pat Perez 69 69, Seung-yul Noh (Kor) 70 68, Stewart Cink 70 68
139 Cameron Tringale 74 65
140 Tiger Woods 72 68, Charley Hoffman 72 68, Marc Leishman (Aus) 70 70, Bo Van Pelt 67 73
141 Ryan Palmer 74 67, Martin Laird (Sco) 72 69, Jhonattan Vegas (Ven) 71 70, Jason Day (Aus) 69 72
142 Nick Watney 70 72, Adam Scott (Aus) 75 67, Bobby Gates 74 68, John Mallinger 70 72, Billy Hurley III 69 73, J.B. Holmes 72 70, Trevor Immelman (Rsa) 74 68, Brandt Jobe 70 72
143 Brian Davis (Eng) 74 69, Sang-moon Bae (Kor) 75 68, Greg Chalmers (Aus) 72 71, Patrick Cantlay 72 71, Daniel Summerhays 70 73, Troy Matteson 73 70, Charles Howell III 70 73
144 Bud Cauley 73 71, Andres Romero (Arg) 73 71, Chez Reavie 72 72
145 Beau Hossler 71 74, Greg Owen (Eng) 70 75, Brian Harman 72 73, Kevin Chappell 72 73, Harris English 71 74, Charlie Wi (Kor) 70 75, George McNeill 73 72, Sean O'Hair 73 72, John Huh (Kor) 72 73
146 Erik Compton 73 73, Martin Flores 75 71, K.t. Kim (Kor) 72 74, Davis Love III 70 76, Gary Woodland 72 74, Heath Slocum 76 70, James Driscoll 70 76, Dustin Johnson 70 76, Ricky Barnes 74 72, Justin Leonard 75 71, Jim Furyk 73 73, Ryuji Imada (Jpn) 72 74, Hunter Haas 74 72
147 Bryce Molder 78 69, Rory Sabbatini (Rsa) 74 73, Kyle Stanley 72 75, Vaughn Taylor 71 76, Chris Di Marco 76 71, J.J Killeen 72 75, Blake Adams 72 75, Brendan Steele 71 76, Ben Crane 77 70, Roberto Castro 74 73, D.J. Trahan 75 72
148 Jeff Overton 79 69, Ben Curtis 74 74, Will Claxton 73 75, Graham Delaet (Can) 74 74, William McGirt 72 76, J J Henry 77 71, Bob Estes 74 74, Arjun Atwal (Ind) 76 72, Brendon Todd 72 76, Y.E. Yang (Kor) 76 72, Ryan Moore 73 75
Missed the cut:
149 Danny Lee (Nzl) 78 71, Robert Allenby (Aus) 75 74, Lucas Glover 80 69, Johnson Wagner 73 76, Matt Bettencourt 75 74
150 Tim Herron 75 75, Billy Mayfair 74 76, Angel Cabrera (Arg) 71 79, Chris Couch 76 74, Tom Pernice Jnr. 78 72, Kevin Streelman 76 74, Michael Thompson 75 75, Cameron Beckman 75 75, Tom Gillis 73 77, Jordan Spieth 75 75
151 Spencer Levin 77 74, D.A. Points 73 78, Kevin Stadler 76 75, John Merrick 77 74, Notah Begay III 76 75, Scott Piercy 76 75, Josh Teater 74 77
152 Kris Blanks 80 72, Kyle Reifers 75 77, K J Choi (Kor) 79 73, Boo Weekley 75 77
153 Chris Kirk 76 77, Brian Gay 73 80, Dicky Pride 76 77, David Mathis 78 75, Camilo Villegas (Col) 78 75
154 Chad Campbell 75 79, Sung Kang (Kor) 77 77
155 Jeff Maggert 78 77
156 Kelly Kraft 74 82
159 Nick O'Hern (Aus) 82 77
160 Mark Anderson 83 77
161 Tommy Gainey 75 86
DQ: Danny Lee (Nzl) 78 71
