By Simon Cambers
Russian Dementieva, beaten in the Paris final in 2004, meets Italy's Francesca Schiavone, while Jankovic, the U.S. Open runner-up in 2008, plays Australian Sam Stosur.
In the 2004 final, Dementieva's nerves got the better of her and she won only four games against compatriot Anastasia Myskina.
The fifth seed has reached the semi-finals of all four grand slams but hopes she can cope with the pressure better this time round.
"You cannot think about winning a grand slam, it's a two- week competition and anything can happen," Dementieva said. "I'm just glad to be in the semi-finals. Let's see if I can handle this challenge."
Seventh seed Stosur knocked out four-times champion Justine Henin and world number one Serena Williams on her way to the semi-finals for the second successive year.
"She's beaten two really good players, Justine and Serena, which shows she's in top form," fourth seed Jankovic said.
"I just want to go out there and play my game and give my maximum, and what happens, happens."
(Editing by Ed Osmond; to query or comment on this story email firstname.lastname@example.org)