Samantha Stosur and Zhang Shuai were apart for more of 2021 than they were together. Between Australia's quarantine rules keeping Stosur at home and Zhang teaming up with Xu Yifan to target the Tokyo Olympic Games, the good friends were able to play only four tournaments together.

They won half of those, including a second Grand Slam title at the US Open, and take an 11-match winning streak as a team into the Akron WTA Finals Guadalajara. It will be their second straight appearance at the year-end finale together. In 2019 they reached the semifinals, losing to Timea Babos and Kristina Mladenovic. In her three previous appearances, Stosur won the championship twice, in 2005-06 alongside Lisa Raymond, and a semifinalist in 2009 with Rennae Stubbs. 

Australia: Opening defeats

With a win in their first Grand Slam title together on Stosur's home soil at the 2019 Australian Open before parting ways at the end of that season, the pair reunited for this year's Australian swing. It did not go well. They lost in the first round of the Gippsland Trophy to Arina Rodionova and Storm Sanders, and the first round of the Australian Open to Leylah Fernandez and Heather Watson.

Stosur did not rejoin the tour for another four months, in which time Zhang performed solidly with partners including Xu and Eri Hozumi. Stosur, meanwhile, reached the Olympic quarterfinals with Ellen Perez.

Summer hard courts: American ascendancy

When Stosur and Zhang reunited again after the Olympic Games, it was a different story. In Cincinnati, they survived super-tiebreaks in their first four matches, saving match point against Anna Blinkova and Aliaksandra Sasnovich in the semifinals. But they passed those tests and were able to defeat Gabriela Dabrowski and Luisa Stefani 7-5, 6-3 in the final to capture their third title together.

Champions Corner: After US Open win, Stosur and Zhang aren't done yet

Stosur and Zhang took that form into the US Open for a spectacular run to the title. They dropped just one set, to Coco Gauff and Caty McNally in the final. It was a feelgood run that bolstered both of their trophy cabinets - but even more than that, it gave the team an unexpected opportunity to extend their partnership.

Road to WTA Finals, singles

Road to WTA Finals, doubles

"It's certainly kept us going for another year," Stosur said. "I didn't know what was going to happen next year. I knew I wanted to play Australia and then after that, who knows? Now that we're winning Grand Slams, it certainly makes you want to keep going even more."