Samantha Stosur has scored a rare win over Maria Sharapova, a spot in the Pan Pacific semi-finals and improved her chances of featuring in the WTA’s end of season event after a big afternoon in Tokyo on Thursday.

Holding a 10-1 career record against the Australian, Sharapova was a heavy favourite in their quarter-final but Stosur emerged a 6-4 7-6 (12-10) winner over the two-time champion.

Stosur broke Sharapova to go up 5-3 in the second set but then lost nine straight points as Sharapova sent the match to a tiebreaker, which Stosur won when Sharapova’s return was long.

The win boosts the world No.9’s chances of an appearance at the WTA Championships in Turkey which is limited to the top eight ranked players in the world.

With current world No.8 Li Na losing to Caroline Wozniacki in a third round match and Stosur only having to defend points from making the last 32 of the tournament last year, the 2011 US Open champion is still well in the reckoning for the prestigious event.

Stosur will face Nadia Petrova of Russia on Friday for a spot in the final.

Petrova beat sixth-seeded Sara Errani of Italy 3-6 7-5 6-3.

Sharapova wasn’t the only top player to bow out.

Top-ranked Victoria Azarenka withdrew after a bout of dizziness in her third-round match on Wednesday, advancing Angelique Kerber of Germany to the semis.