Petra Kvitova (CZE #7) vs.  Maria Kirilenko (RUS #15)
Head-to-head: series tied 3-3
Worryingly for the rest of the draw, Petra Kvitova is showing signs of returning to the sort of form that saw her sweep all before her in her breakthrough season back in 2011. Her quick-fire victory over Klara Zakopalova on Tuesday was her eighth in succession and took her into the quarterfinals at Indian Wells for the first time.
Her opponent there, Maria Kirilenko, though, will be feeling equally chirpy after disposing of No.3 seed Agnieszka Radwanska in a three set thriller. Kirilenko has been one of the WTA's most improved players over the past year or so and, when on song, her cerebral game and fit-as-a-fiddle physique is a match for most.
Kvitova found this out to her cost at last summer's Olympics, when she was out-maneuvered and out-thought on the recently re-laid All-England Club lawns. But, she did not have to wait long for revenge, turning the tables a few weeks later in the New Haven final.
 Sara Errani (ITA #8) vs.  Maria Sharapova (RUS #3)
Head-to-head: Sharapova leads 2-0
Maria Sharapova and Sara Errani met twice last season - both came on the biggest stage and both ended in comfortable wins for the Russian. With Wednesday evening's encounter taking place on her favored outdoor hardcourts, Sharapova will be heavily fancied to stretch that head-to-head superiority and reach a third consecutive semifinal of the season in the process.
In Francesca Schiavone, Carla Suárez Navarro and Lara Arruabarrena, Sharapova's route to the quarterfinals has prepared her well for the challenge presented by Errani, who possesses a tireless engine and a deceptively aggressive baseline game.
However, as her ranking suggests, Errani is a step up from the aforementioned trio. No player in 2013 has won more matches than the super-fit Italian - number 21 coming over Marion Bartoli in the last 16 - and with temperatures expected to scale 80°F, Sharapova will be well aware of the dangers of getting dragged into a war of attrition.