Spain's Garbine Muguruza reached the semifinals of the season-ending WTA Finals in Guadalajara, Mexico, after beating Anett Kontaveit, while Karolina Pliskova missed the cut despite her comeback victory over Barbora Krejcikova on Sunday.
Muguruza ended Kontaveit's 12-match winning streak with a 6-4, 6-4 win over the Estonian, booking a spot in the knockout stage for the first time since her tournament debut in 2015.
Muguruza won a remarkable 80 per cent of her first serve points and fired seven aces in Sunday's victory as she finished second in the "Teotihuacan Group" behind Kontaveit, with both posting a 2-1 record.
"Today was a match that was kind of everything or nothing," Muguruza told reporters. "Starting the round-robin with a loss, it was never good. To finally get two wins and qualify was amazing."
Two-time Grand Slam champion Muguruza will face compatriot Paula Badosa in Tuesday's semifinal. The winner of the contest will be the first Spanish woman to reach the final since Arantxa Sanchez Vicario finished runner-up in 1993.
"I didn't know all of this history," Muguruza said. "1993, I was born that year.
"It's amazing that there are four players left and two of them are Spaniards. That just shows that Spain has a great level of tennis."
Earlier, Pliskova came out on top in an all-Czech showdown, storming back to stun compatriot Krejcikova 0-6, 6-4, 6-4.
Despite the win, Pliskova failed to reach the semifinals as she finished third in the group, with Kontaveit and Muguruza advancing as the top two. Second-seeded Krejcikova ended bottom after losing all three matches.
The WTA Finals divides the top eight players into two groups of four, with each player competing in three matches. The top two from each group advance to the semifinals.