Federer upset by 27th-ranked Stepanek in Rome quarters

Roddick also reached the semifinals in his debut at the Foro Italico in 2002, losing to Tommy Haas. His semifinal opponent this time will be Stanislas Wawrinka, who rallied past eighth-seeded James Blake 6-7 (5-7), 7-6 (7-5), 6-1.

The last American to win in Rome was Andre Agassi in 2002.

Roddick improved to 8-0 against Robredo, rushing the net on both his first and second serves against the Spaniard.

"He's a better clay-court player than I am, so I just attacked and, let's face it, I had to volley better than I have in my whole life," Roddick said.

In the third-set tiebreaker, Roddick overwhelmed Robredo with two aces and converted his first match point after following his second serve to net. Federer surrendered a 5-2 lead in the second-set tiebreaker, and wasted a set point at 6-5 on Stepanek's serve by hitting into the net.

Federer had won four of his previous five meetings with Stepanek, but the pair are now 2-2 on clay.

"He's difficult to play," Federer said. "He's always changing his game up a lot. But I've played him in the past, so it wasn't a surprise. I just wish I played better."

Stepanek converted his second match point with a first serve that Federer couldn't return. In the first-set tiebreaker, Stepanek took control with a volley to go up 6-4, then served an ace on his first set point.

After his illness, Federer responded by winning Estoril and reaching the final of the Monte Carlo Masters in his last outing, losing to Nadal. Federer pronounced himself fully fit at the beginning of this tournament, and his problem Friday didn't appear to be physical.

At one stretch of the first set, Federer won four straight service games without losing a point. Still, Stepanek kept up the pressure with his serve and volley.

"If you let him play his game, he can move the ball all around the court," Stepanek said. "I wanted to keep the pressure on."