PARIS: Serena Williams kept alive her hopes of making Grand Slam history in Paris on Friday, but she was again well below her best in a 7-6 (9/7), 6-4 French Open semi-final win over Kiki Bertens.

For the second straight day, the 34-year-old American looked out-of-sorts and at times exasperated before finally clawing her way back to stay alive.

She will now play Garbine Muguruza in Saturday's final with the prize for her being a 22nd Grand Slam title, equalling the Open-era record set by Steffi Graf in Paris in 1999.

The fourth seeded Spaniard underlined her fine form with a 6-2, 6-4 win over Australia's Samantha Stosur.

“The first set was not simple, but she was playing so well,” Williams said.

“I need to keep my calm for the final and hope the fans will be with me.”

Williams already looked out-of-sorts in her quarter-final on Thursday against 60th ranked Yulia Putintseva, having to claw her way back from a set and a break down to get through.

And it was another ponderous start from the three-time former winner against her 58th-ranked, opponent, losing the first three points of the match and dropping her serve.

Bertens, who had never made it past the fourth round of a Grand Slam tournament prior to Paris, went 2-0 up before Williams opened her account.

The cold, damp conditions were similar to Thursday and the atmosphere was muted on a less-than-half full Philippe Chatrier centre court.

Williams was having trouble returning the Bertens serve and she had to save break points on her own to avoid falling further behind.

The Dutchwoman failed to convert a set point at 5-3 with Williams serving and then a pair of drop shots in the next game brought up a break-back point for the American which she converted with a big forehand drive.

Bertens appeared to be having trouble with an injury to her left calf muscle as Williams took the lead for the first time in the match, but she held firm to force a tie-break.

In that, Williams eased ahead 5-2 after losing the first point on her serve, but two botched volleys at the net saw her hand a set point back to Bertens before she found some form to take it 9/7.

The pair exchanged service breaks to get the second set underway and Bertens then failed to take two break points to get to 4-2.

She paid the price for that minutes later as Williams grabbed the break she needed to put the match away needing four match points in the end.

The final will be the fourth match in four days for Williams due to the bad weather that has dogged Roland Garros this week.