Paris, France (SportsNetwork.com) - World No. 1 great Serena Williams looked every bit the part in Wednesday's quarterfinal action at the 2015 French Open.

The powerful 33-year-old American star blew away 17th-seeded Sara Errani 6-1, 6-3 to reach only her fourth career semifinal at Roland Garros.

The reigning Australian and U.S. Open champion Williams, who owns a pair of French Open titles (2002, 2013), had to rally from a set down in each of her last three matches, but it was a walk in the park for her on Court Chatrier on Day 11 of the fortnight.

"I wasn't able to serve well in my first couple of matches here because I hurt my arm in Madrid, and in Rome I had to pull out," Williams said. "In my first few matches I thought maybe I shouldn't serve too big, but now I'm feeling a little better. It's obviously a big part of my game -- I really missed it a lot."

Williams struck 39 winners, including 10 aces, compared to zero aces for Errani, who has recorded the weakest serve of this fortnight, while Williams has struck the hardest.

Williams is now 9-0 lifetime versus Errani.

"The last four French Opens in a row she's been to the quarterfinals or better, so I knew I had to be really focused today," Williams said. "She does so well here, and she really fights for every point."

The soft-hitting Italian Errani was the French Open runner-up in 2012 and played in her fourth straight French Open quarterfinal. She had won 19 of her last 22 matches here.

Williams, who's now 30-1 this year, is seeking her 20th Grand Slam singles titles. Only Margaret Court (24) and Steffi Graf (22) own more. Helen Wills Moody, like Williams, also owns 19 major championships, but they all came during the Amateur Era (before 1968).

Williams' semifinal opponent on Thursday will be 23rd-seeded Swiss Timea Bacsinszky, who defeated upstart Belgian Alison Van Uytvanck 6-4, 7-5 on Court Lenglen.

Van Uytvanck hadn't faced a seeded player in the draw until Wednesday. Both she and Bacsinszky were appearing in their first major quarterfinal.

Williams is 2-0 versus the 25-year-old Bacsinszky, including a straight-set quarterfinal win at Indian Wells back in March.

The other semi will pit seventh-seeded former world No. 1 Ana Ivanovic against 13th-seeded Czech left-hander Lucie Safarova. The Serbian Ivanovic was the French Open champion in 2008 and runner-up in 2007.

Safarova is 5-3 lifetime versus Ivanovic, but the Serb won their last meeting in Tokyo last year. They've split a pair of meetings at the French, with Ivanovic winning in the second round in '08 and Safarova returning the favor in the third round last year.