Isner used his booming serve to win the first-set tiebreaker.

"Four months ago, I was unranked," Isner said. "To go from that to beating Roger Federer in a set is pretty cool."

Federer quickly figured Isner out and kept up his bid for a fourth straight Open title.

"I started to pick up on his serve for the second set," Federer said.

Fifth-seeded Andy Roddick breezed, beating 2002 Australia Open champion Thomas Johansson of Sweden 6-3, 6-2, 6-0 to reach the fourth round.

"I've got to try to find myself a hot date later," said Roddick, who's dated actress Mandy Moore and been linked to Sharapova in the past, "so I tried to get off the court a little faster."