INDIAN WELLS, CA, USA - A day after No.1 seeds Cara Black and Liezel Huber were defeated at the BNP Paribas Open, No.2 seeds Nuria Llagostera Vives and María José Martínez Sánchez were eliminated in what has turned out to be an upset-ridden fortnight in the doubles competition.

Sixth-seeded Bethanie Mattek-Sands and Yan Zi survived the Spaniards in a match tie-break, 76(3) 16 105. Mattek-Sands and Yan played just one event together in their careers prior to Indian Wells, but they were impressive, losing a three-setter to eventual champs Serena and Venus Williams in the quarterfinals of this year's Australian Open. As for Llagostera Vives and Martínez Sánchez, after a terrific 2009 that saw them collect a Tour-best seven titles - including the season-ending Sony Ericsson Championships - they are off to an inconsistent start to 2010, having won Dubai, but losing in the round of 16 at the Australian Open and now the quarters here.

Wednesday's other quarterfinal saw No.3 seeds Nadia Petrova and Samantha Stosur also record a victory in a match tie-break, 26 62 107, over unseeded Iveta Benesova and Barbora Zahlavova Strycova. It's no surprise that Petrova and Stosur - playing their third career event together - were tested, as the Czechs were fresh off their second title of the year in Monterrey.

So while Mattek-Sands and Yan will take on Petrova and Stosur in one semifinal, the other will be a battle of unseeded teams - Chan Yung-Jan and Zheng Jie versus Kveta Peschke and Katarina Srebotnik.