SHENZHEN - Home player Zhang Shuai and her Australian partner Samantha Stosur powered into the semi-finals of the Shiseido WTA Finals Shenzhen here on Thursday by defeating Czech duo Barbora Krejcikova/Katerina Siniakova 6-3, 7-6 (7) in their purple group round-robin clash.

Each side came into the clash with on win and one loss in the purple group, but their Czech opponents stood above them in the group on set difference.

Each side held its opening service game before Stosur/Zhang got the first break off a pair of unforced errors from the Czechs.

Stosur/Zhang then held their next service game to love, and both sides would go on to hold their services to 4-2 for the China-Australia duo, who got a second break to go up 5-2 only to see their opponents convert a triple break point.

Undeterred, Stosur/Zhang quickly raced to a 40-30 lead on the Czech's next service, getting a crucial third break to seal the set in just over half an hour. Stosur/Zhang played a clutch first set, committing only three unforced errors to nine winners.

Things start out well for the local player and her partner during the second set. The Czech duo converted a triple break point on the way to Stosur/Zhang dropping their opening service. They would be broken once more as the Czechs built up a 4-0 lead.

But Stosur/Zhang fought back admirably, erasing the deficit and getting to breaks of their own to pull level at 5-all. Their returning game was especially strong; they shot 71 percent on the way to equalizing and converted two of the three break points they created after their initial stumble out of the gate. Each side would then serve out the remainder of the set to force a tiebreak.

The second set tiebreak was just as closely fought, with the two sides getting an equal number of breaks to go 7-all before some stellar returning from Stosur/Zhang put them ahead and they went on to stitch up the match in one hour, 40 minutes.

"We had a really good beginning in the first set, very aggressive. All of the preparation, all the tactics were implemented. During the match, at the very beginning, there were many points that were very close. Three or four times we could have won the points. We encouraged each other because we knew they were playing really well," Zhang said in the post-match press conference.

"In the second set, we wanted to be as aggressive as we were in the first set. We could have done better. We were also surprised when we were down 1-5. We were able to overturn the score. Our opponents were very strong with very good serves. I think my partner did really, really well today. That is the key to our success," she concluded.