(CNN) -- Marathon man John Isner survived another epic on his return to competitive tennis after his record-breaking 11-hour Wimbledon match. The American saved two match points before beating Gilles Muller, from Luxembourg, 4-6 7-6 7-6 to seal his place in the quarterfinals of the Atlanta Tennis Championships. It is Isner's first tournament since Wimbledon back in June when his opening round victory over Frenchman Nicolas Mahut in London clocked in as the longest match in tennis history. Isner's battle with Mahut stretched over three days and 183 games before he finally triumphed, 6-4 3-6 6-7 7-6 70-68. He later told CNN: "I really didn't think it was going to end."
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John Isner wins on first outing since his record-breaking Wimbledon tournament
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Isner defeats Luxembourg's Gilles Muller 4-6 7-6 7-6 in Atlanta
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25-year-old took part in the longest tennis match in history at Wimbledon
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Isner beat Frenchman Nicolas Mahut in an 11-hour match that ran for three days
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