John Isner put on a serving clinic at the ATP 500 event in Memphis yesterday, firing 26 aces in his 7-6, 7-6 victory over Gilles Muller.

The American was unstoppable on both his first and second serves, and Muller simply couldn't find any rhythm on his return.

"It was a match I knew was going to be tough," Isner, who recently beat Roger Federer, said after the match. "I knew I was going to have to scrap it out. I served my best, so that helped."

In other action, Ryan Sweeting defeating ailing countryman James Blake 6-0, 6-2, while Sam Querrey beat Alejandro Falla 2-6, 6-3, 6-4.

Ryan Harrison also advanced, beating Jack Sock 6-3, 2-6, 6-4.