Stepanek will face Australian Open champion Novak Djokovic after Spain's Nicolas Almagro withdrew from their quarter-final with a wrist problem with the score at 6-1, 1-0 to the Serb.

World number one Federer, struggling for consistency on clay ahead of the year's second Grand Slam later this month, was the second big gun of the day to fall to an unseeded player after his Swiss compatriot Stanislas Wawrinka won an entertaining tussle with American James Blake 6-7, 7-6, 6-1.

Federer was comfortable on his service games in the first set of the quarter-final, taking four to love, but he failed to force any break points. Stepanek wrapped up the ensuing tiebreak 7-4 with an ace as the Swiss lost a set for the first time in the tournament.

A fired-up Stepanek saved two break points in the first game of the second set and then snapped the top seed's serve immediately after.

The Swiss broke back in the seventh, only to surrender his serve again the following game, a wild shot giving away the vital point. He dragged himself back in contention two games later, the counter-break coming courtesy of a beautiful backhand volley.

But Federer was unable to capitalise on two mini-breaks in the tiebreak and will now have to wait at least another year for his first Rome title.