Serena Williams French Open 2015 Quarterfinals
Serena Williams celebrates her passage through to the French Open semifinals after a comfortable win over Sara ErraniReuters

World number one Serena Williams crushed Italian Sara Errani 6-1, 6-3 to reach the semifinals of the French Open in intimidating fashion on Wednesday.

The twice Roland Garros champion set up a meeting with Swiss 23rd seed Timea Bacsinszky, who beat Belgian Alison van Uytvanck 6-4, 7-5.

American Williams hammered 39 winners in a one-sided encounter against the diminutive 17th seed Errani, a French Open runner-up in 2012.

"I knew I had to start better today than the other days because she's a tough opponent who's got history here," Williams told a courtside interviewer in French.

She had lost only two sets in eight victories from as many matches against Errani, but the Italian pushed her to the limit in their last encounter in the Fed Cup in April.

Williams had dropped the opening set in her previous three rounds but was quickly out of the blocks on Wednesday, setting the tone by breaking in Errani's first service game.

A brilliant backhand passing shot handed Errani an immediate break back but Williams was in the groove and dominated the rest of the opening set.

Errani upped her pace in the second as she looked quicker on her feet, but it was still not enough as Williams broke for a 4-3 lead and she finished it off on her fourth match point.