WIMBLEDON, England (AP) — Roger Federer leaned on the net, exhausted but exhilarated after winning the final set 19-17 to earn his first Olympic singles medal.

"It has been a long time coming," he said.

The wait included an Olympic marathon yesterday, when Federer played for four hours, 26 minutes to beat Juan Martin del Potro of Argentina 3-6, 7-6 (5), 19-17. It was the longest three-set men's match of the Open era.

"I definitely got a sense that it was something special," the top-seeded Federer said. "The deeper we went into the match, the more I thought, 'Wow, this is so cool to be part of a match like this'."

Federer converted only two of 13 break-point chances, the second coming in the next-to-last game, and had several nervous moments. But he held serve 12 times in the final set to stay in the match.

With the comeback victory, the four-time Olympian is assured of at least a silver. Tomorrow he'll play in the final against number three Andy Murray of Britain, who beat number two Novak Djokovic of Serbia 7-5, 7-5.

Federer beat Murray on the same court in the Wimbledon final a month ago.

In 2008, Federer and Swiss teammate Stanislas Wawrinka won the gold in doubles. But Federer had been O for three in Olympic singles, the biggest blemish on a resume that includes a record 17 Grand Slam titles.

Americans Bob and Mike Bryan are assured of at least a silver after beating Julien Benneteau and Richard Gasquet of France 6-4, 6-4 in the semi-finals of men's doubles. Mike Bryan and Lisa Raymond advanced to the first Olympics mixed doubles final since 1924 by beating Del Potro and Gisela Dulko 6-2, 7-5.

For duration, Federer's latest victory didn't rival John Isner's 70-68 final-set win at Wimbledon in 2010, or even Jo-Wilfried Tsonga's 25-23 win in the third set at the Olympics this week. But the match offered epic drama magnified by the setting and the stakes for Federer.

He improved to 12-0 this summer at the All England Club, including a record-tying seventh Wimbledon title a month ago.

There were no match points until the final game. After a couple of wobbly moments by Federer, including a double-fault, he sealed the victory when Del Potro dumped a backhand in the net.

Federer lifted his arms in jubilation, then leaned wearily on the net while awaiting congratulations from the big Argentine. They shared a warm embrace.

"I felt for him in a big way," Federer said, "because I've been there as well."

Said Del Potro: "It's not an easy situation. Someone always has to win these matches, and today it was his turn."

Del Potro will play Djokovic for the bronze tomorrow.