Rome, Italy (Sports Network) - World No. 1 superstar Roger Federer suffered a quarterfinal setback Friday at the hands of gritty Czech Radek Stepanek at the $3.5 million Italian Masters. Meanwhile, Australian Open champion Novak Djokovic and former top-ranked star Andy Roddick avoided upsets in order to reach Saturday's semifinals at this clay-court French Open tuneup.

The 27th-ranked Stepanek stunned the top-seeded Federer in straight sets in a pair of tiebreaks, 7-6 (7-4), 7-6 (9-7), at Foro Italico. Federer was the runner-up at this event in 2003 and 2006.

Stepanek pulled off the upset in 1 hour, 55 minutes with the help of eight aces and a pair of service breaks.

The 29-year-old Stepanek is now 2-4 lifetime against Federer, who had won their previous four meetings, including a third-round one here in 2006.

The 12-time Grand Slam champion Federer dropped to 22-6 this season and has captured only one title in seven tournaments thus far in 2008.

The third-seeded Djokovic was dismantling Nicolas Almagro 6-1, 1-0 when the Spaniard retired due to a right wrist injury. The Serbian Djokovic is now 23-5 this year and will battle Stepanek here on Saturday.

A sixth-seeded Roddick outlasted 14th-seeded Spaniard Tommy Robredo 6-3, 4-6, 7-6 (7-4) in 2 hours, 13 minutes. The massive-serving American, who fired 11 aces and piled up seven double faults on Day 5, improved to 24-4 this year, including a pair of titles.

Up next for Roddick will be Swiss Stanislas Wawrinka, who recorded an upset by besting eighth-seeded American James Blake 6-7 (5-7), 7-6 (7-5), 6-1. Wawrinka will break into ATP's top-20 as a result of his semifinal appearance here.

This week's winner will take home $558,000.