Much like in her quarterfinal match the day before, Williams struggled to find her form early on, making 22 unforced errors in the first set alone. Some reports claim the American is struggling with an abductor injury.

Unseeded Dutch player Bertens had two set points in the opener at Roland Garros but couldn't convert and Williams' experience told as she triumphed in a tie break before taking the second set 6-4 and setting up a repeat of the 2015 Wimbledon final match up with Muguruza.

After the match, Williams didn't reveal much about any fitness concerns:

"I have had some issues, but it will be survival of who can do the best," she said of the final. "I want to do well and I would like to win tomorrow. But Muguruza has been playing really well, with an aggressive game and going for her shots.

"I think it will be a good match, the last time we played here in France she was able to win. But I learned so much from that match"

Muguruza, 22, impressed in a relatively comfortable 6-2, 6-4 win over Australian veteran Sam Stosur in cold conditions.

Aside from a few nerves when serving for the match, the youngster dominated throughout, combining speed, power and skill at the net to defeat Stosur.

Williams has won three of her four meetings with Muguruza's, with the Spaniard'S only victory coming in the second round at this tournament in 2014.

The final will be Williams' latest attempt to pull level on the 22 grand slam singles titles of Steffi Graf. She has failed to win her last two majors in New York and Melbourne.

mp (AP)