World number one and defending champion Novak Djokovic was knocked out of the Madrid Masters yesterday, losing 7-6 6-3 to Janko Tipsarevic.

Djokovic’s quarter-final defeat comes a day after Rafael Nadal was defeated by fellow Spaniard Fernando Verdasco in the third round.

Tipsarevic earned only his second career win against Djokovic, who beat him last February in a quarter-final in Dubai.

He claimed the 61-minute opening set on a tiebreaker, then remained collected as Djokovic saved three match points in the eighth game of the second set before losing a game later as Tipsarevic came through on his fourth opportunity.

Earlier in the day, Serena Williams routed Maria Sharapova to reach the semi-finals, but insisted she has no intention of joining Nadal and Djokovic in their blue clay boycott threat.

The American ninth seed cruised to a 6-1, 6-3 quarter-final win over second-seeded Sharapova.

Williams said that while the blue clay courts remain problematic, the issue was not enough to make her consider skipping the event in 2012.

“This is a tough surface and it’s extremely slippery but if I’m not here next year, it won’t be because of the clay,” she said.

“This is not the best court – definitely not what they play like at Roland Garros. But it’s what they use at Madrid. Maybe next year they’ll put more clay on it.

“When it’s hot, it gets more slippery. But that’s an element you cannot control and it goes for every clay court.”

OTHER Quarter-finals: (Women) Azarenka bt Li Na 3-6 6-3 6-3; Radwanska bt Lepchenko 6-4 6-4; Hradecka bt Storus 7-6 7-6.

(Men) Del Potro bt Dolgopolov 6-3 6-4; Berdych bt Verdasco 6-1 6-2; Federer bt Ferrer 6-4 6-4.