BETHESDA, Md. — A punishing golf course. Temperatures that topped 100. Hunter Mahan still managed to make Friday at the Congressional Country Club feel like a breeze.
    Mahan finally had a good score to match the efficient way he has been swinging the club. He made seven birdies in the stifling heat for a 6-under 65, giving him a two-shot lead going into the weekend at the AT&T National as he goes after a PGA Tour-leading third win of the year.
    Chris Couch sought medical attention and struggled to finish in the oppressive conditions. One caddie had to stop after nine holes, and another vomited to the side of the 13th green from drinking too much water.
    Tiger Woods stayed in the game with a 68 in the morning, when it was still so hot that towels were used to wipe sweaty faces more than to clean clubs. He talked about the value of staying fit and strong to survive days like this. He was five shots behind.
    Mahan, though, has set himself apart for two days.
    "I hit a lot of good shots," said Mahan, who missed only two fairways and three greens. "I hit so many fairways and greens, I made it easy on myself. This is a pretty punishing golf course if you get off line a little bit. I put myself in some great spots to make putts. And I felt like I played well on the back, when it was getting really hot and you're getting a little bit more tired."
    Mahan was at 7-under 135. His two rounds fulfilled what his swing coach, Sean Foley, said Thursday when describing his ball-striking as "a laser show."
    Robert Garrigus had his sixth straight sub-par round at Congressional — that includes last year at the U.S. Open when he became a footnote in history as only the fourth American to break par all rounds of a U.S. Open — with a 67 and was two shots behind, along with Jimmy Walker and Brendon De Jonge, who each had a 69.
    Stewart Cink, who draped a towel over his head waiting his turn to putt on the 14th green, showed signs of a resurgence with a 68 that put him in the group three shots behind, along with Vijay Singh (70), Pat Perez (69) and Rod Pampling (67).
    Woods was at 2-under 140, in a tie for 11th.
    More telling than only 18 players who remained under par was the cut at 148. It was one shot higher than the cut for the U.S. Open last year at  Congressional, and it was the highest score to make the cut at a regular PGA Tour event since 149 at The Barclays in 2009.
    Congressional was tough — fast and firm on the course, scorching in the air — but it was fair.
    Mahan twice had to save par over the last five holes. He came up short on the 14th, but he had a couple of options. With the pin all the way to the back behind a ridge, he could run it up the slope to the hole, or even play long and have it roll back to the hole. He chose to lag it to the hole, hit it thin, and got away with the slight miss when it rolled back to 2 feet.
    "I expected to hit it a little bit cleaner off the club face, but that how you shoot 65," he said. "Get good breaks like that."
    He was more pleased with the 17th, which he called the one loose swing of the day. Mahan missed the green to the right, but saved par. On the 18th, he ripped a tee shot and had sand wedge into the green to 12 feet for one last birdie.
    Woods was as happy about two pars as he was with his 50-foot eagle putt on the 16th hole that put him under par for the first time all week.
    He was in trouble early after a few tee shots were caught in the dense rough that makes the Congressional feel like a U.S. Open and forced him to hack out short of the green. Both times, he hit wedges that landed by the hole, bounced 15 feet by and caught the slope to come back within 3 feet.
    "The pars at 14 and 15 were something I needed to have happen," Woods said. "I hit two good wedge shots in there after two poor drives and gave myself a couple good looks, made those, and then I rewarded all that hard work at the next hole with eagle."
    Woods was three shots behind when he finished, and didn't expect to fall back much farther. The course, already looking like it was supposed to play last year for the U.S. Open, was getting firm and crusty from the scorching heat. It was the kind of day reminiscent of when Ken Venturi won the 1964 U.S. Open at Congressional, so dehydrated he almost didn't finish. And high heat was expected well into the weekend, making this a test of survival.