Swiss tennis player Stanislas Wawrinka has reached the semi-finals of the Rome Masters while number one Roger Federer was knocked out of the tournament.

Wawrinka beat eighth-seeded James Blake 6-7 (5), 7-6 (5), 6-1, propelling the Swiss into the top 20 of the ATP rankings. Federer lost 7-6 (4), 7-6 (7) to Radek Stepanek, who is 27th in the world.

"It's my first Masters Series semifinal, so I'm very pleased," Wawrinka said.

Blake missed an easy volley to hand Wawrinka a break in the first game of the third set and the Swiss rolled home from there.

Wawrinka called for a trainer to treat his lower back with a 6-5 lead in the second set, then again with a 2-1 lead in the third, but the problem did not appear to affect his play.

The Swiss number two also reached the semi-final of the Barcelona Open last weekend, losing to David Ferrer.

Wawrinka will next face either No. 6 Andy Roddick or No. 14 Tommy Robredo.

Stepanek won the first match against Federer in a tie-break and had a four-one lead in the second. Federer fought back but the Czech player held on.

The Rome Masters is an important clay-court warm-up for the French Open, which begins on May 25.

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