The first-round match at Wimbledon took 11 hours, 5 minutes over three days.
American Isner closed out the victory this morning (NZT) with a backhand winner, then collapsed to his back as he tossed his racket in jubilation and relief.
Isner won 6-4, 3-6, 6-7 (7), 7-6 (3), 70-68.
The match lasted so long it was suspended because of darkness two nights in a row. Play resumed today at 59-all and continued for more than an hour before Isner won.
The American finished with 112 aces, and Mahut, of France, had 103. There were only three service breaks in the match, the last coming on the final point.