Roger Federer and Juan Martin del Potro, mountaineers of tennis

LONDON -- Just when you think Roger Federer has climbed his last peak in tennis, he clips on the crampons and heads for the top of Everest.

Friday, in the men’s Olympic tennis semifinals, the air got pretty thin where the world’s No. 1 player went. He reached yet another pinnacle of drama and success.

After 4 hours and 26 minutes of superb serving and shot-making, a record for a three-set match in men’s singles in the modern era, Federer had outlasted Argentina’s Juan Martin del Potro. The score was 3-6, 7-6 (5), 19-17, and when they walked to the net for the handshake at the end, the dazzled crowd at Wimbledon’s Centre Court gave them the kind of full-throated tribute prompted by moments of true greatness.

Del Potro was magnificent. Federer was a tad better. Del Potro won 180 points, Federer 186. The big-serving Del Potro, 6-foot-6, hit 11 aces. The sneaky-quick-serving Federer hit 24.

It was to be a day of two men’s and two women’s semifinals, sharing the aura of Wimbledon’s Centre Court. It started with Federer and Del Potro shortly after noon. Serena Williams and Victoria Azarenka didn’t even go on until after 5, and that was followed in twilight by the local feature, Britain’s Andy Murray versus Serbia’s Novak Djokovic, where the home crowd carried Murray to a 7-5, 7-5 dazzler, and into a repeat of the Wimbledon final against Federer.

Williams continued her scorched-earth run to the gold medal, dismissing Azarenka of Belarus, the No. 1 women’s player, 6-1, 6-2. The other women’s semifinal was played on Court 1 — lucky for them — and Maria Sharapova beat Russian Olympic teammate Maria Kirilenko, 6-2, 6-3.

As compelling as the other matches were, Federer-Del Potro turned them into afterthoughts.

Del Potro had stunned Federer with a five-set victory in the 2009U.S. Openfinal and also won their next meeting. But since then, a resurgent Federer had won their last six meetings, including a 6-3, 6-2 walk-in-the-park at Indian Wells this year.

But this time was Ali-Frazier. Nobody backed off. No quarter was given.

On and on it went. The previous record for men’s three-setters was 4 hours, 3 minutes by Djokovic and Rafael Nadal in the ’09 Madrid final. Federer and Del Potro slugged their way past that easily. During the match, the weather changed four times, toddlers learned how to walk, governments changed dictators and lunchtime gave way to cocktail hour.

Del Potro broke Federer’s serve at 3-3 of the first set, Federer got a look at a break point early in the second set and after that it was big-serving dominance into the tiebreaker. It was much the same in the third, with the exception of the strange exchange of breaks, starting with Del Potro toeing the line at 8-8. Federer broke with a forehand winner and that seemed like a certain end. But Federer inexplicably lost his service game at love, and they played on for nearly 11/2 more hours.

At 17-17, Del Potro played three loose points, faced love-40, saved two break points and finally succumbed by netting a backhand. Federer, serving from behind the entire third set and now getting his second chance to serve for the match, got it to 40-30 but netted a volley. Then, on Federer’s next match point, Del Potro finally blinked on a big point, netting a backhand.

Federer, the worm that will not quit wiggling, went to the net, leaned on it and waited for Del Potro.

“He was sad, very touched,” Federer said afterward. “I told him to be proud, that he played a great match.”

Federer said he was spurred by the knowledge that a victory would give the Swiss their first medal here. He spoke with reverence about the Olympics, which has a special history for him.

He met his wife, Mirka Vavrinec, at the Sydney Games. She was then a tennis player from Slovakia, now the mother of his twin girls. He lost a bronze-medal match there to Frenchman Arnaud di Pasquale, then lost early in Athens to Tomas Berdych of the Czech Republic and in a Beijing quarterfinal to American James Blake.

Federer has won Olympic gold in doubles. A victory Sunday would put him in the special company of, possibly, only Williams, with titles in all the majors, plus singles and doubles Olympic gold.

Federer, 31 on Aug. 8, is a resume-filler. Olympic singles gold is the lone remaining blank.

bill.dwyre@latimes.com