PARIS (AFP) - Having seen her main rivals fall by the wayside, Serena Williams is the overwhelming favourite to win a third French Open title as she prepares to face Timea Bacsinszky in Thursday's semi-finals.

The 33-year-old American, who is looking for a 20th Grand Slam title, produced her most powerful performance yet to sweep past Italian 17th seed Sara Errani 6-1, 6-3 in the quarter-finals on Wednesday.

She will now hope her far greater knowledge of the big occasion gives her the edge against Bacsinszky.

The 23rd seed from Switzerland beat unseeded Belgian Alison van Uytvanck 6-4, 7-5 to build on her fourth-round victory against Wimbledon champion Petra Kvitova, the fourth seed, and win through to her first Grand Slam semi-final.

"She's a good player. I think most of all about her is she's a major fighter. You can have match point, be up a set, and she's not going to give up," said Williams of a player she has beaten in each of their two previous meetings, including in the quarter-finals at Indian Wells this year.

"She's had a really good year. It's not going to be an easy match at all for me.

"I need to come out strong again. Most of all I need to relax.

"If I win, great. If I lose, I want to be able to do the best that I can do.

"I'm not putting too much pressure on myself."