Maria Sharapova rallied to earn a spot in the semi-finals of the Madrid Open, a few hours after defending champion Serena Williams withdrew from her match because of injury.

In the men's draw, Rafael Nadal gave his clay-court doldrums a boost by easing through to the last-four as well.

Sharapova, who lost to Williams in last year's final, beat Li Na 2-6, 7-6, 6-3 on clay at the Magic Box.

Meanwhile, Williams, the top-ranked American, has had her thigh heavily bandaged during play at the clay-court event, and said the injury occurred during a first-round victory over Belinda Bencic on Sunday.

"It started to get better but, most importantly right now, I just need some time to rest and recover," Williams said in a statement. "It's beyond words. It's so frustrating. This is not the way I wanted this week to end."

The withdrawal gave 2011 champion Petra Kvitova a walkover victory and a spot in the semi-finals.

The 32-year-old Williams said the injury would not keep her out of the French Open, with the defending champion tweeting she would play in Rome next week before the second Grand Slam of the season starts on May 25.

Nadal, the top-ranked Spaniard, had lost his previous two quarter-final matches on clay for his worst run on the surface in a decade. But buoyed on by a partisan crowd, Nadal beat Thomas Berdych 6-4, 6-2.

Source: Reuters