GUADALAJARA, Mexico -- In a battle between the reigning Roland Garros and Wimbledon champions, No.1 seeds Barbora Krejcikova and Katerina Siniakova dropped just four games to No.3 seeds Hsieh Su-Wei and Elise Mertens, winning 6-3, 6-1, to stay undefeated at the Akron WTA Finals Guadalajara and secure a spot in the semifinals.

Now 2-0 in the El Tajín group, Krejcikova/Siniakova secured their advancement to the semifinals after No.6 seeds Alexa Guarachi and Desirae Krawczyk defeated No.8 seeds Sharon Fichman and Giuliana Olmos, 0-6, 6-3, [11-9]. The Czech team's qualifying position will be determined on Monday when the group completes round robin play. 

Despite their dual successes this season, Saturday's match-up between Krejcikova/Siniakova and Hsieh/Mertens was a first-time meeting, pitting the two winning teams from the opening round of group play against each other. The Czech duo defeated Fichman/Olmos 6-4, 6-1, while Hsieh/Mertens prevailed 7-6(3), 6-2 over Guarachi/Krawczyk. 

Krejcikova is doing double duty this week in Guadalajara, as the first woman to qualify for the WTA Finals in singles and doubles since her countrywoman - and next singles opponent - Karolina Pliskova in 2016. Meanwhile, Siniakova can finish the season at doubles No.1 pending their progress through the tournament. 

The Czechs' resilience would ultimately form the basis for their dominance on Saturday. Krejcikova, who played a tough three-set singles match against Garbiñe Muguruza less than 24 hours earlier, was nearly broken in her first two service games. But the Czech team dug themselves out of trouble, holding from 0-30 down twice, as Krecjikova/Siniakova won two key deciding points to stay unbroken early in the first set.

"Today was an amazing match. I think we played really great," Siniakova said. "I was just trying to help Bara because it's really hard for her and I think she's doing an amazing job."

After breaking Hsieh's serve to lead 3-1, the Olympic champions never looked back, saving all five break points they faced in the match and breaking Hsieh/Mertens four times. Despite Krejcikova's fatigue, the Czechs were the better team in the clutch, winning five of the six deciding points in the match. They won 82% of their first serve points and landed 17 winners to just 7 from Hsieh/Mertens.

"I'm playing every single day and every single day the atmosphere gets better," Krejcikova said. "I've been playing with Katerina for a very long time. It's very special that we can play together and be really successful and outside of the court we can be friends and things are working out for us."

Guarachi and Krawczyk were the only team who needed a win to avoid elimination. That looked unlikely for a first set in which they were thoroughly dominated by Fichman and Olmos. The Canadian-Mexican pair were looking for their first win of the tournament and, backed by enthusiastic crowd support, surged through a bagel set in which they conceded only nine points.

After Guarachi and Krawczyk got a foothold in the match with improved serving, the key moments of the second set came in the fifth and eight games. At 2-2, Krawczyk faced down two break points on her serve, with a sharp Guarachi poach sealing the hold. The Chilean-American duo then broke Fichman for 5-3 after Olmos netted a volley on deciding point.

The super-tiebreak came down to the wire, with neither team getting more than two points clear of the other at any juncture. Ultimately, Guarachi and Krawczyk were firmer at its climax, with Krawczyk putting away a smash to seal their third match point.

With Krejcikova and Siniakova through to the last four, Monday's play will find each of the three remaining teams still in with a shot at joining them. Guarachi and Krawczyk need to defeat Krejcikova and Siniakova and for Fichman and Olmos to defeat Hsieh and Mertens. Fichman and Olmos need to defeat Hsieh and Mertens in straight sets and for Krejcikova and Siniakova to defeat Guarachi and Krawczyk. Hsieh and Mertens can advance either by defeating Fichman and Olmos, or with a three-set loss if Krejcikova and Siniakova beat Guarachi and Krawczyk.