John Isner, competing in his first tournament since Wimbledon, defeated Gilles Muller of Luxembourg 4-6, 7-6 (6), 7-6 (7) last night at the Atlanta Tennis Championships. Isner became a household tennis name after winning a three-day marathon over Frenchman Nicolas Mahut at the All England Club last month, prevailing 70-68 in the fifth set in the first-round epic. The No. 2-seeded American, who received a first-round bye, was playing his first match since losing to Dutchman Thiemo de Bakker in the second round at Wimbledon. Isner seems to have a habit of playing lengthy matches. The Mahut match took a record 11 hours and five minutes. Yesterday’s three setter lasted two hours and 33 minutes. Muller, who is ranked No. 206 and had to qualify for the main draw, blasted 29 aces and never lost his serve. Isner, the ATP Tour leader in aces with 705, had 33 and dropped serve once. “With Gio as my opponent, he’s probably one of the last guys I want to play,” Isner said. “First match back (against) a big-serving left-hander, he’s not going to give you much rhythm. So that was a little bit working against me, but I just told myself to compete.” Isner saved two match points — one with a deft forehand drop volley at 5-6 in the second-set tiebreaker and the other with a service winner down 6-7 in the third-set tiebreaker. “This win was huge,” the No. 19-ranked American said. “Maybe one of the biggest of the year because I wanted to get some matches under my belt before going on to (Washington) D.C. and the two Masters Series events and the U.S. Open.” Isner won his first ATP Tour title at Auckland in January and was runner-up at Memphis in February and Belgrade in May. Sam Querrey defeated the 6-foot-9 Isner in both finals. Isner improved to 25-15 on the year and a tour-best 23-12 in tiebreakers.