Agnieszka Radwanska (POL #5) vs.  Caroline Wozniacki (DEN #12)
Head-to-head: Wozniacki leads 5-4
Despite being rivals on the court, Caroline Wozniacki and Agnieszka Radwanska have always managed to remain friends off it. This friendship dates back to their junior days and has survived the test of time, not to mention nine matches against one another.
While Wozniacki - who was the first to fully establish herself in the senior ranks - won the majority of their early meetings, recent bragging rights are Radwanska's. The last three encounters have all gone the Pole's way and she will fancy her chances of extending this run.
Last week, Radwanska played her best tennis of the year to triumph in Montréal, and has carried this form south of the border, looking particularly imperessive in swatting aside Sabine Lisicki in the last round.
 Simona Halep (ROU #2) vs. (5) Maria Sharapova (RUS #6)
Head-to-head: Sharapova leads 4-0
WTA Rising Star Simona Halep may have missed the first two weeks of the summer hardcourt season, but there has been no sign of rustiness in her opening matches at the Lindner Family Tennis Center.
Straight set victories over Kirsten Flipkens and Lucie Safarova have taken her safely through to the quarterfinals, where she will renew acquaintances with Maria Sharapova, who she lost out to in the finals of Madrid and Roland Garros.
On both those occasions, Halep had her chances and she is looking forward to taking their rivalry onto the cement. "I want to play against her because I want to see if on hard she will beat me again," Halep said. "I just want to try my game, to play very aggressive, to open the angles like always, and to stay very focused."
Stat to watch: Halep trails Sharapova by 116 points on the Road To Singapore leaderboard and will rise to the top with victory in their last eight match-up.
Also on court...
Serena Williams continues her bid for a maiden Cincinnati title when she takes on Jelena Jankovic in the second up on Center Court. The evening match sees No.9 seed Ana Ivanovic take on the tournament's surprise package, Elina Svitolina.