Madrid - Swiss split the difference as Roger Federer posted a quick win in less than an hour while Stan Wawrinka laboured for three times that long in a third-round loss to Juan Del Potro at the Madrid Masters Thursday.

Second seed Federer, trying to whip his clay game into top shape with Roland Garros starting a week from Sunday, crushed American James Blake 6-2, 6-4 to win his ninth match of 10 played in that series. Blake, seeded 14th and a surprise finalist last weekend on clay in Estoril, won his only encounter at the Beijing Games, their last meeting.

Monte Carlo semi-finalist Wawrinka went down in two hours, 58 minutes after letting his chances slip against fifth seed Del Potro of Argentina.

The Swiss swept the opening set then nearly came back from a double break down in the second as he saved five set points but was felled on a sixth from the South American racket.

Wawrinka lost a break in the deciding final set and then struggled to save four match points over two games before finally sending a return wide.

Britain's Andy Murray took another step in his bid to challenge for the world number two ranking as he put out Spanish 16th seed Tommy Robredo 7-5, 6-1 to reach the quarter-finals.

Murray only reached a career-best third in the world on Monday as he overhauled Novak Djokovic for the spot.

"I got a bit too passive but the second set was much better«" said the Scot. "Robredo can make you run, I couldn't go trying for many winners form behind the baseline."

Murray now stands 2-2 apices against Robredo and 31-4 on the season. He was unable to convert on eight break points in his opening set.

He will Friday face Del Potro after having beaten the Argentine five times including twice on clay. (dpa)