It set the stage for a thrilling finale to the match which had the atmosphere of a Davis Cup tie, with Swiss cowbells jingling around the stands and chants of “Roger” ringing out.
A cool Federer served to stay in the match at 4-5 and then pounced to gain the decisive break for 6-5.
Even then Del Potro looked like forcing a deciding tiebreak, but Federer would not be denied and belted down his 10th ace to complete a remarkable victory.
“I don’t get a day off, I’ve got to back it up and be ready to go again tomorrow,” Federer said. “I’ll try to make his [Nadal’s] life a bit difficult.”
Del Potro was left to rue a match that got away, but was encouraged by his return to the top five after some injury-plagued years since winning the 2009 US Open.
“I think I’m doing great matches against the top guys,” said 25-year-old Del Potro, who has posted wins against Nadal, Djokovic, Andy Murray and Federer this year. “I think I am the only player who beat all of them in this season, which means something for me.”