Congressional Country Club is demanding enough in benign weather, with its gnarly rough and slick greens presenting one hitch after the other. Throw in searing temperatures and oppressive humidity, and the course that’s hosted three U.S. Opens and a PGA Championship becomes that much more unforgiving.

As golfers concluded their rounds on Friday at the AT&T National, much of the conversation turned not to the condition of the Blue Course but how best to withstand a heat index that reached 109 degrees by 4 p.m. and had the PGA Tour allowing caddies to forgo wearing bibs.

Jimmy Walker was among the fortunate players who teed off early in the morning before haze enveloped the grounds. Walker shot a 2-under 69 for a two-day total of 137, two strokes behind leader Hunter Mahan.

“We’ve been doing this a long time,” Walker said. “We know how to battle through the heat and stay hydrated. . . . It’s the fans you’ve got to worry about because they’re out walking around, and they don’t get into this type of stuff and get out and walk in it too much. They’re the ones that have really got to do a good job about hydrating.”

Many fans sought refuge under trees while liberally consuming water and sports drinks. A heavily shaded area by the clubhouse pro shop was a favorite spot for rest breaks for countless spectators bathed in perspiration and heading to the parking shuttles.

Centreville resident Brendan Lau was among the diehards who braved heat warnings to follow tournament host Tiger Woods. Lau estimated he consumed only three bottles of water over the course of the afternoon.

“Liquor, about four,” he said.

“I feel like I’m sweating in places on my body that I didn’t know could sweat,” said Lau’s wife, Junghye Choe.

So severe was the heat that PGA Tour player Chris Couch, who stands 6 feet 4 and weighs 225 pounds, needed medical attention at the 15th hole. Despite drinking roughly 25 bottles of water and three Gatorades in addition to taking salt pills, Couch said he felt as if he were near passing out.

Couch complained of extreme headaches and even experienced chills. Medical professionals checked Couch’s blood pressure, which was slightly elevated. Soon after, he was cleared to finish his round and wound up missing the cut.

“I never like to quit,” said Couch, 39. “I was close to the cut line. I birdied 16. I think it’s just difficult for everyone. I talked to Ryan Moore. He said when he was bending over he had headaches also. I think everybody’s getting a little bit of it out there.”

The sweltering conditions were reminiscent of when Congressional hosted the U.S. Open in 1964. Temperatures reached triple digits on the final day, when at the time the USGA mandated 18 holes in the morning and another 18 in the afternoon.

Barely able to get around the course because of dehydration, Ken Venturi etched his name into golf lore with a resounding comeback that included overtaking 54-hole leader Tommy Jacobs, who began the final round two strokes in front.

Venturi also passed Arnold Palmer on his way to winning his first tournament in four years while in the company of, among others, a physician administering salt tablets and ice packs, one marshal with an umbrella to shield the sun’s rays, the USGA’s executive director, a uniformed police officer and playing partner Ray Floyd.

“You play well in the heat because you don’t think about it,” said Robert Garrigus, whose second-round 67 left him in a three-way tie for second with Walker and Brendon de Jonge at 5 under. “It’s one of those things where if you can just get past the fact you’re dripping sweat all over your golf ball, you can block it out.”

Then there’s Woods, whose longstanding dedication to exercise and conditioning makes him among the most physically fit athletes in the world. Woods followed a first-round 72 with a 3-under 68 to move within five shots of the lead with a weekend of excessive heat and humidity in the forecast.

“That’s why I train. That’s why I run all those miles,” the 14-time major champion said. “If you’re carrying a little bit of body fat, it’s going to be a little insulation out there. This is when fitness does help, and I figured that’s one of the reasons why I’ve had the success I’ve had in the elements.”

Staff writer Barry Svrluga contributed to this report.