The 16-time Grand Slam champion was playing in a first-round Davis Cup tie for the first time in eight years and was doing so in front of his hometown fans in Firbourg, Switzerland. But a fast, sloppy clay surface left him frustrated before the match and Isner's powerful serve kept him that way during it, leading to a stunning four-set, 4-6, 6-3, 7-6 (4), 6-2 victory for the American.
It was the first time Federer had lost to an American on clay since 1999 and his first Davis Cup loss in 15 matches.
Isner's win gave the United States a 2-0 lead in the opening-round tie. Earlier in the day, Mardy Fish outlasted Stanislas Wawrinka in five sets, winning 9-7 in the last. The Americans are playing without an injured Andy Roddick and Bob Bryan, who is back in the states caring for his newborn daughter.
Federer got a break early in the first set and cruised to a 6-4 win. Despite 12 more break chances in the match, the world No. 3 wouldn't get another. Isner's serve was predictably solid, but he won the match on his passing shots and at the net. The uneven surface allowed the American to get behind shots and change angles, crossing up Federer countless times during their match.
The final two points of the match captured the overall tenor of play. On two Federer second serves, Isner took a step inside the baseline and unleashed a crosscourt return backhand that Federer barely reached for.
"It's the biggest win of my life, that's for sure," Isner said after the match. "But what it means to me is that our team is up 2-0."
Saturday's doubles match is scheduled to pit Federer and Wawrinka against Fish and Ryan Harrison.
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- Roger Federer
- John Isner