Novak Djokovic became the latest big name to lose on the new blue-clay court at the Madrid Open, going down 7-6 (2), 6-3 to Janko Tipsarevic in an all-Serb quarter-final on Friday.

It was Tipsarevic's second win in five matches against Djokovic, who last lost at this stage of a tournament in November at the Paris Masters.

Second-ranked Rafael Nadal was beaten by Fernando Verdasco on Thursday, while second-seeded Maria Sharapova lost to Serena Williams in the women's event earlier on Friday.

Boycott

Following his loss, Nadal said he would not return to the tournament unless it reverts to red clay. Djokovic said the same, describing the new surface as slippery.

While Djokovic had little trouble holding serve early on, Tipsarevic saved four break points to force the first-set tiebreaker.

The seventh-seeded Tipsarevic broke the defending champion early in the second set, closing it out after Djokovic had saved three match points.

Also, Juan Martin del Potro served 10 aces in beating Alexandr Dolgopolov of Ukraine 6-3, 6-4. The Argentine will play Tomas Berdych in the semi-finals.

The six-seeded Berdych won 6-1, 6-2 over Verdasco, who made 24 unforced errors and showed little of the flair on display against Nadal.

On the women's side, Williams brushed aside Sharapova 6-1, 6-3 to advance to the semi-finals along with top-ranked Victoria Azarenka.

Williams opened strongly, serving six aces and earning two early breaks to take the first set. Sharapova finally showed some fight and broke to love to level at 2-2 in the second set, but she quickly squandered her break with a costly sixth double fault to fall behind and ultimately lose to Williams for the seventh straight match.

Williams, who improved to 11-0 on clay this year, will face Lucie Hradecka after the Czech upset US Open champion Sam Stosur 7-6 (8), 7-6 (6).

Azarenka win

Azarenka joined Nadal and Djokovic in their criticism of the blue clay court saying she felt 'unstable' [GALLO/GETTY]

Azarenka overcame a shaky start to beat French Open winner Li Na 3-6, 6-3, 6-3.

Azarenka struggled initially with her serve but broke her Chinese opponent's first two service games of the second set en route to levelling the match.

Azarenka, who has won four titles this season and was last year's runner-up in Madrid, used her powerful groundstrokes to jump out to a 4-0 lead in the decider before holding off Li's late charge.

"She was pretty unbelievable in the first set,'' said Azarenka.

"I had to turn something around. I don't know if it was confidence or if it was self belief or just pushing myself to be better and really wanting to win the match.''

Azarenka said she agreed with Nadal and Djokovic in their criticism of court's surface.

"You feel unstable sometimes. Actually, a lot of times,'' she said.

"But right now there is no point on talking about it. After the tournament all the players can get together and discuss it.''

The Belarusian will next face fourth-seeded Agnieszka Radwanska, who beat Varvara Lepchenko 6-4, 6-4.

Source: AP