In temperatures that topped 100 degrees, Mahan ran off seven birdies Friday afternoon for 6-under-par 65 in the AT&T National. It was the best score of the week at Congressional, and it gave him a two-shot lead over Robert Garrigus, Jimmy Walker and Brendon De Jonge.
Tiger Woods got back in the mix with 68 in the morning, though Mahan made his weekend task a little tougher. Mahan made birdies on two of the last three holes to reach 7-under 135, leaving Woods five shots behind.
The heat was so stifling that Chris Couch struggled to finish, one caddie had to stop after nine holes and another threw up from drinking too much water.