Top-seed John Isner, playing for the first time since helping the U.S. defeat Switzerland in Davis Cup, defeated Gilles Muller of Luxembourg, 7-6 (1), 7-6 (4) in the Regions Morgan Keegan Championships on Tuesday.

Isner, ranked a career-best No. 13 in the world, overpowered Muller with 26 aces, including five in the two tiebreakers. Isner also won 96 percent of his first-serve points. The 26-year-old advances to the second round where he'll oppose American Donald Young.

"Even though I beat Roger (Federer), it was just one match," Isner said. "I think confidence comes from putting a string of match (wins) together. I haven't really played that many matches. This was just my seventh match of the year."

Isner's doubles partner, Sam Querrey advanced to the second round with a 2-6, 6-3, 6-4 victory against Alejandro Falla of Colombia on Tuesday.

Querrey underwent right elbow surgery in June and won for only the second time this year in five matches. His world ranking has dropped to 99th after peaking at No. 17 in January 2011.

"I feel pretty close," Querrey said of returning to match shape. "I'm missing more forehands than I usually do, but I'm just committed to stepping up and hitting it. More and more are falling (in) every day."

In other men's first-round matches, James Blake, participating in his first ATP Tour match since encountering knee problems late last fall, dropped a 6-0, 6-2 decision to fellow American Ryan Sweeting.

In a late match, top-seed John Isner, ranked a career-best No. 13 in the world, plays in the opening round against Gilles Muller. No. 2 seed Andy Roddick opens defense of his Memphis title Wednesday night.

Querrey's first-round victory added to his history of success in Memphis. He improved to 13-4 overall. He has advanced to at least the quarterfinals four of the past five times in Memphis.

Querrey survived falling behind a break in the third set and won with an ace, his 12th, on match point.

In the Memphis International, the accompanying Women's Tennis Association event, No. 2 seed and Russian-born Ksenia Pervak defeated Canada's Rebecca Marino, a finalist in last year's tournament, 6-2, 6-4, in first-round play.

Unseeded Varvara Lepchenko, who became a U.S. citizen in September, upset No. 7 seed Johanna Larsson of Sweden, 6-2, 6-4, to move into the third round along with No. 5 Pauline Parmentier of France. Parmentier defeated Andrea Hlavackova of the Czech Republic, 6-4, 4-6, 6-2.