INDIAN WELLS, CA, USA - The final two semifinal spots at the BNP Paribas Open will be decided on Thursday as Samantha Stosur takes on Angelique Kerber and defending champion Victoria Azarenka meets Caroline Wozniacki.
 Angelique Kerber (GER #6) vs.  Samantha Stosur (AUS #9)
Head-to-head: Stosur leads 2-0
Remarkably, for such an accomplished hardcourt player, Samantha Stosur has only once been beyond the quarterfinals at either Indian Wells or Miami. On Thursday morning, she will attempt to add to that tally when she takes on one of last year's semifinalists, Angelique Kerber.
That run - eventually ended by Victoria Azarenka - was one of a number of reputation-enhancing showings by Kerber in a season that would culminate in a first ever Top 5 finish. But, prior to touching down in California, the German had been enduring something of a sophomore slump, compiling a disappointing 7-5 record since January.
A relatively kind draw - she is yet to face an opponent inside the Top 30 - has allowed Kerber to play herself into form this fortnight, winning all three matches without dropping a set. As impressive as these performances were, though, how she deals with Stosur's top-spin loaded groundstrokes on the high-bouncing surface out on Stadium 1 is likely to provide a far more accurate gauge of just where her form is at.
Stosur is certainly match tough, having been pushed to three sets by both Peng Shuai and Mona Barthel, and arguably has the psychological edge owing to the victories in her two previous matches with Kerber, at the US Open in 2011 and last year's Fed Cup.
 Victoria Azarenka (BLR #2) vs.  Caroline Wozniacki (DEN #10)
Head-to-head: Wozniacki leads 4-2
Two years ago, Caroline Woznaicki and Victoria Azarenka met in the quarterfinals at Indian Wells. That occasion ended in anticlimax, a hip injury forcing Azarenka to retire just three games in. The players, who have been rivals since their days on the junior circuit, have not met since.
A lot has changed in the intervening period; Azarenka's star has soared - winning two majors and spending 51 weeks at the top of the rankings - while Wozniacki's fortunes have taken a turn for the worse.
The Dane, who was top seed and eventual champion at Indian Wells in 2011, may no longer be the player to beat on tour, but her competitive fire burns as bright as ever. She proved this in coming from a break down in the final set of her second round match with Alizé Cornet and has followed this up with tidy wins over Elena Vesnina and Nadia Petrova.
Aside from a slight hiccup against Kirsten Flipkens, Azarenka's progress has been similarly smooth, stretching her unbeaten start to the season to 17 matches. More concerning than any of her opponents, however, has been a nagging ankle injury, which is sure to be given the most thorough of examinations by Wozniacki and her famed retrieval skills.