John Isner wins in straight sets at Winston-Salem Open

John Isner shook off a slow start to beat fellow American Bradley Klahn 7-6 (7-5), 6-2 on Tuesday in the second round of the Winston-Salem Open.

Isner, the tournament's top seed and two-time winner, served 13 aces - one clocked at 138 mph - and broke Klahn's serve twice in the second set to improve to 11-0 all-time in the final tuneup before next week's US Open.

Three of the top six seeds were eliminated in the second round at the Wake Forest Tennis Center. Third-seeded Tommy Robredo of Spain lost to France's Nicolas Mahut 6-1, 7-6 (7-0); fourth-seeded Leonardo Mayer of Argentina was upset by Belgian qualifier David Goffin 6-3, 6-1; while Poland's Jerzy Janowicz stunned No. 6 seed Joao Sousa of Portugal 6-1, 3-6, 7-6 (7-5).

However, No. 2 seed Kevin Anderson of South Africa overcame a shaky second set to beat France's Adrian Mannarino 6-3, 2-6, 6-4.

The 6-foot-8 Anderson, ranked 20th in the world, served 16 aces and almost as many service winners. Mannarino used his ground game to force Anderson into 24 errors in the second set, breaking his serve twice en route to taking the set and evening the match at 1-all. But Anderson got a key service break in the seventh game of the third set, and closed out the match with two aces and a service winner in the deciding game.

Robredo, the tournament's third seed, had his serve broken three times in the first set by the 104th-ranked Mahut, who then took four mini-breaks from Robredo in winning the second-set tiebreaker.

"I knew he was in for a tough week after Cincinnati," Mahut said of Robredo, who had upset world No. 1 Novak Djokovic of Serbia in advancing to the quarter-finals of last week's Western and Southern Open. "I knew if I had a good start, it would be difficult for him. The second set was tougher, but it was still a good finish. I had to play more aggressive in the tiebreak, but it was still good."

Goffin, who won his first ATP Tour event last month in Kitzbuhel, Austria, extended his winning streak to 24 matches. That includes ATP Challenger Tour event wins in the Netherlands, Poland and Finland.

Also advancing were Americans Sam Querry and Donald Young, Edouard Roger-Vasselin of France, Italy's Andreas Seppi, Spain's Marcel Granollers, Kazakhstan's Mikhail Kukushkin, Taiwan's Yen-Hsun Lu, Lukas Rosol of the Czech Republic, and Spain's Pablo Andujar.