FORT WORTH, Texas -- Top seeds Barbora Krejcikova and Katerina Siniakova opened their title defense on Day 1 at the WTA Finals with a 6-4, 6-3 win over No.8 seeds Desirae Krawczyk and Demi Schuurs in round-robin play.

No.3 seeds Coco Gauff and Jessica Pegula were unable to avoid the upset later in the night session, losing to No.6 seeds Xu Yifan and Yang Zhaoxuan 6-4, 4-6, 10-7. 

The champions at three of the four majors this season, Krejcikova and Siniakova extended their win-loss record to 24-3 this year. The Czech duo won their first WTA Finals title last fall in Guadalajara, and are bidding to become the first team to go back-to-back at the season-ending championships since Timea Babos and Kristina Mladenovic in 2018 and 2019. 

After six holds of serve to open the match, Krejcikova and Siniakova were the first team to break to 4-3. After being broken back, the Czechs broke again to 5-4 and Krejcikova served out the set. 

The second set was dominated by the returners, as the teams combined for five consecutive breaks of serve to open the set. Krejcikova finally broke the streak, holding serve on a pitch-perfect lob to extend their lead to 4-2. It was a lead the Czechs would not relinquish, as they broke Krawczyk and Schuurs off two missed volleys and closed out the match after 1 hour and 30 minutes. 

"I think we've been playing solid tennis from both sides," Krejcikova said. "The first match is always difficult. I expected it would be tricky and we would have a lot of tough moments. There were many [deciding points], which I think we did really well. I think that was key."

Xu and Yang defeat Gauff and Pegula

To close out the night session, Indian Wells champions Xu and Yang continued their trend of success on American soil to join the No.1 Czechs at the top of the Nancy Richey group. In their third meeting of the season, the Chinese duo avenged their recent loss in San Diego to earn their second win of the season over the Americans. 

Xu and Yang are the first all-Chinese team to play the WTA Finals since Yan Zi and Zheng Jie in 2006. The duo was the sixth team to qualify for the event this year, securing their spot in the final week of the season en route to the Guadalajara semifinals. 

Xu and Yang came through a tight opening set that was decided by just one break. Gauff and Pegula struggled to generate break-point chances, going 0 for 1 in the opening set. Xu and Yang took control in the early stages of the second set, grabbing an early break to lead 3-1. But the Americans battled back to take the set 6-4 and force a match-tiebreak.

But the Chinese pair withstood the momentum shift that seemed to favor the Americans, overcoming an early mini-break at 2-1 to break back and seize control for good. 

Rosie Casals Group standings