Istanbul, Turkey, 25 October 2012 | AFP/AAP

Sam Stosur has received a last minute call-up to play in the WTA Championships after defending champion Petra Kvitova pulled out of the tournament complaining of a viral condition.

The Czech player lost her opening match in round robin play on Tuesday to Poland’s Agnieszka Radwanska, going down 6-3 6-2.

With a match already played and lost it leaves Stosur with the difficult task of having to win both her matches to progress to the semifinals.

Stosur will face world No.2 Maria Sharapova and No.7 Sara Errani in the scheduled remaining matches for her group.

The championships feature the top eight ranked players in the world. Stosur has been elevated from first reserve as she was ranked No.9 before the tournament began.

She directly qualified for the championships in 2010 (when the event was contested in Doha) and last year in Istanbul, and both years reached the semifinals.

Last year it was Kvitova who ended her run with a three-set win in the penultimate match.