The 17-time Grand Slam champion and Stan Wawrinka swept aside Julien Benneteau and Richard Gasquet 6-3, 7-5, 6-4 in the doubles to put Switzerland into a 2-1 lead against France in the Davis Cup final on Saturday.
Federer can secure the decisive point against Jo-Wilfried Tsonga in the first reverse singles on Sunday. If Tsonga wins, Wawrinka and Gael Monfils will decide the final.
Despite a humbling straight-sets loss to Monfils on the opening day, the 33-year-old Federer put his back problems behind him to produce a superb display against a French pair that failed to seize its chances in the second set.
"I'm fine now. I understand you want to know everything about (my back). But I know as much as you do," said Federer, who picked up the injury last week at the ATP Finals. "I've been very open and honest. For me, it's just about now, whatever it feels like, I feel like I am at 100 per cent. I'll give it 100 per cent."
Federer and Wawrinka, who won doubles gold at the 2008 Olympics, ended a four-game losing streak in Davis Cup at the right time, and posted their first win together in the event in three years. It was also their first doubles win on clay.
"I think the way we prepared mentally for this doubles match was different. We know that we are able, when we play well, to beat the top players," Wawrinka said.
With drums, cowbells and cheers creating a deafening atmosphere in the converted Pierre Mauroy Stadium, Wawrinka and Federer did not concede a single break and dominated the key points to withstand their opponents' charge in the second set.
"They played extremely solid. Roger served incredibly well. Their second shots were extremely efficient. They made no mistakes. They never made mistakes," summed up Benneteau, a doubles specialist who won the French Open this year. "At the net, Stan was extremely good. He didn't miss much. And we played against two exceptional servers."
Marco Chiudinelli and Michael Lammer were initially set to play but Swiss captain Severin Luthi changed his lineup after Federer was deemed fit.
His French counterpart Arnaud Clement stuck to his decision to send in Gasquet and Benneteau, and brushed off speculation that he was forced to rest Tsonga because of an injury. Tsonga and Gasquet trained together earlier Saturday, and Clement was bombarded with questions on his main player's condition.
"Imagine if there was something, I wouldn't tell you anyway," Clement said. "Of course, I can just say that Jo rested today for some reasons, and there will be no problems tomorrow."
French Tennis Federation president Jean Gachassin later told French TV that Tsonga was doubtful for Sunday's singles because of pain in an elbow.
Federer's prediction that he would play better in the doubles was right, as he served and moved far better. The Swiss duo converted their dominance to break for a 4-2 lead in the first set when Wawrinka unleashed a powerful forehand that Gasquet could hardly touch.
With Federer improving as the match progressed, they sealed the set in just 28 minutes but were offered a tougher challenge in the second. The French returned better yet failed to seize their opportunities as the former Olympic champions saved five break points.
Federer did not look annoyed by his back at all, hitting some acrobatic smashes and stretching for volleys while racing forward and back with ease.
Benneteau saved two break points with two consecutive winners in the ninth game but Gasquet then showed his nerves when he was let down by his serve two games later. The Swiss made no mistake and converted the first one, with Wawrinka firing a forehand down the line that sent the Swiss fans into rapture.
Put on the ropes, the French fended off four break points early in the third set but another stunning forehand passing shot from Wawrinka gave the Swiss the decisive break in the fifth game.
"We came on the court to take that point, we were aggressive, we knew what we had to do, and we did a good job," said the fourth-ranked Wawrinka. "We know each other so well."