Maria Sharapova and Serena Williams reach Madrid Open semis

Serena Williams and Maria Sharapova remain on track for a battle over the world number one ranking after both made the Madrid Open semi-finals.

Russian world number two Sharapova will replace Williams on top if she betters the American's showing in Spain.

She recorded a routine 6-2 6-4 victory over Kaia Kanepi in the last eight.

Williams, who had not previously dropped a set, was given a scare by Spanish wildcard Anabel Medina Garrigues before winning 6-3 0-6 7-5.

"It was definitely a battle," said 30-year-old Williams, who committed nearly 50 unforced errors against clay-court specialist Medina Garrigues in an encounter which lasted two hours and 14 minutes.

"I obviously didn't do much in the second set, and I think I gave her a lot of confidence to play better," she said.

After seeing off the world number 63, Williams will meet Italy's Sara Errani, who beat Russia's Ekaterina Makarova 6-4 6-3, in the semi-finals on Saturday.

"I definitely want to cut back on my unforced errors," added the 15-time Grand Slam champion.

"I think I'm going to go back to the way I have been playing and being more calm and not making as many errors as I did today."

Sharapova's progress was far more comfortable as she saw off world number 51 Kanepi from Estonia.

The French Open champion had to save only one break point during the entire match and will meet Ana Ivanovic in the last four after the Serb's 6-3 6-1 win over Angelique Kerber.