SHENZHEN, China - In a winner-take-all final match for each team, Australian Open champions Samantha Stosur and Zhang Shuai sealed their place in the semifinals of the Shiseido WTA Finals Shenzhen. 

The second doubles team to advance out of the Purple Group, the Aussie and Chinese pair beat last year's finalists, Czechs Barbora Krejcikova and Katerina Siniakova, on Thursday, 6-3, 7-6(7).

Facing a 5-1 deficit in the second set, the veterans came all the way back to seal the match in two sets, and also saved a set point in the tiebreak to avoid going the distance for the third time in three matches. 

"We had a really good beginning in the first set, very aggressive," Zhang told Chinese reporters after the match, via translator.

"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.

"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 are very strong with very good serves.

"I think [Sam] did really, really well today. That is the key to our success. When we are together, we are both very positive. When we look at each other, we always smile as each other.

"When we have each other, we draw strength in each other. We know we can be a really strong team. This is a great support...I feel inspiration and positive energy from her."

After losing their first round robin match to No.2 seeds Hsieh Su-wei and Barbora Strycova on Sunday, the No.7 seeds bounced back to become the second qualifiers out of the group, behind the aforementioned Wimbledon champions.

Hsieh and Strycova, the No.2 seeds, finished Purple Group play with a 2-1 record, as they were defeated by No.4 seeds Gabriela Dabrowski and Xu Yi-fan.

Dabrowski and Xu, already eliminated from knockout contention by losing their first two matches, came from a set down to close out Thursday's play, 2-6, 6-4, 11-9. 

Read more: Hsieh-Strycova seal semifinal spot, Stosur-Zhang notch first win at WTA Finals

"When we saw the draw, or even before the draw, when we looked at the other seven was a very tough draw. It felt like we could not beat any of the teams here," Zhang added. 

"[We] were encouraging each other. I said, We just need to do our best. When we've met those teams in previous tournaments, it was usually in quarterfinals or semifinals.

"We have all the champions of the Grand Slams here, four different teams in the four different Grand Slams. They're here in the Finals. To win each match, we have to beat these champions, these very strong teams.

"We both understand the situation. We have a lot of support from different areas. We're very lucky to be able to make it to the semis."

With three of the four teams in the semifinal lineup now confirmed, Friday's round robin play from the Red Group will decide the last team to advance.

Top seeds Elise Mertens and Aryna Sabalenka and No.8 seeds Anna-Lena Groenefeld and Demi Schuurs are both in with a chance to join No.3 seeds, and defending champions, Timea Babos and Kristina Mladenovic in the final four from the group.