Bacsinszky wants birthday to remember, make Ostapenko's forgettable

French Open semi-finalists Timea Bacsinszky and Jelena Ostapenko both celebrate their birthdays on Thursday but the Swiss star insists she'll be happy to ruin the party for her close friend.

Bacsinszky reached the Roland Garros semi-finals for the second time on Tuesday with a rain-hit 6-4, 6-4 win over home hope Kristina Mladenovic.

Bacsinszky, who also made the last four in 2015, will face unseeded Ostapenko who stunned Danish 11th seed Caroline Wozniacki 4-6, 6-2, 6-2 for a place in Saturday's final.

But Thursday's last-four duel also falls on the day when world number 31 Bacsinszky turns 28 while Ostapenko, ranked 47, is 20.

"It's a nice story, pretty cool," said Bacsinszky who was already aware of the quirk in the calendar.

"We played doubles together in Wuhan last year and we have practised a lot together.

"She's a really nice girl. We saw each other in the gym after today's matches and congratulated each other and hugged.

"Yeah, it's pretty funny we have the same birthday.

"Lucky for her that she's just 20 but maybe lucky for me as I have more experience!"

Bacsinszky, playing in her third successive French Open quarter-final, will be the favourite on Thursday.

Ostapenko has never made the semis of a major.

Before Roland Garros she had never got past the third round.

The Latvian is hoping to become the first player since Gustavo Kuerten at the 1997 French Open to win their first tour-level title at a Grand Slam.

Kuerten's breakthrough triumph at Roland Garros coincidentally came on the very same day that Ostapenko was born.

Bacsinszky, meanwhile, knows what it's like to be on the semi-final stage, going three sets before losing to Serena Williams in Paris in 2015.

"There has always been a kind of magic here for me," said the Swiss star after Tuesday's rain-interrupted match which took almost six hours to complete.

"Even the first time I came here as a little kid, there's been a special bond."

Despite that attachment, she admitted she was struck by nervous anxiety on the eve of Tuesday's quarter-final.

She even woke up in a sweat at four in the morning, dazed by a nightmare that she had left Roland Garros but had forgotten to buy tournament towels for her friends.

"I was sweating over this. I guess if I wasn't playing the big matches in a Grand Slam I wouldn't have these nightmares.

"But it's good to be nervous -- it shows that I am not a robot."

After seeing off Mladenovic, Bacsinszky said the weather conditions which saw heavy rain as well as 30km/h winds had been tough to deal with.

"We had a hurricane, a sandstorm and almost snow," she said before adding that coming from Switzerland, it wasn't hard to adapt.

"I practiced in Bienne a few weeks ago with (Swiss player) Victorija Golubic and it was snowing.

"So heavy clay? I'm used to it. That was an appetizer for today."