Madrid, Spain, 10 May 2012 | AFP

Sam Stosur’s French Open preparations have been boosted as she booked her place in the the quarterfinals of the Mutua Madrid Open with a 6-3 6-2 win over Petra Cetkovska of Czech Republic on Wednesday.

The US Open champion will now face either Czech Lucie Hradecka or Ekaterina Makarova for a place in the semifinals.

China’s French Open winner Li Na is also through to the last eight, beating 12th seed Angelique Kerber 7-5 6-4.

Kerber went down in 85 minutes to Li, who is building momentum on clay as she prepares to defend her title at Roland Garros from May 27.

Li reached the Stuttgart quarter-finals last month in her season debut on the surface.

The winner broke three times on the way to victory, where she will await either top seed Victoria Azarenka or Serb Ana Ivanovic.

In the second round on the blue clay of the Caja Magica, Polish fourth seed Agnieszka Radwanska put an end to the 16-match win streak on clay of Sara Errani with a 6-0 6-1 thrashing in 65 minutes.

Roberta Vinci struck a blow for Italy after Errani’s loss, sending out Belgian Yanina Wickmayer 6-1 6-2.

Errani was fresh from the clay title in Budapest at the weekend.