Paula Badosa, of Spain, hits the ball while playing Aryna Sabalenka of Belarus, during the Mexican Tennis WTA Finals in Guadalajara, Mexico on Nov 11, 2021. (REFUGIO RUIZ / AP)

Paula Badosa overcame a slow start to take down Belarusian top seed Aryna Sabalenka after Maria Sakkari continued her dominance of Iga Swiatek in the round-robin stage of the WTA Finals in Guadalajara, Mexico on Thursday.

I said to myself, okay, now you have to be at her (Aryna Sabalenka) level, aggressive, because she was being very aggressive...I said, "Now you have to change, stop waiting for her miss and go for it". That's what I did.

Paula Badosa, Spanish professional tennis player

Badosa stunned world number two Sabalenka 6-4 6-0 after winning the last 10 games, while Sakkari secured a comfortable 6-2 6-4 win over Poland's Swiatek.

Badosa was 2-4 down in the first set but the Spaniard withstood Sabalenka's early power to take the opening set.

ALSO READ: Badosa outworks Azarenka to win Indian Wells title

The 23-year-old, who lifted the Indian Wells title last month, closed out the match with a bagel in the second set as she celebrated a win under the lights on her WTA Finals debut.

Asked how she bounced back from her shaky start, Badosa said, "I said to myself, okay, now you have to be at her level, aggressive, because she was being very aggressive...I said, 'Now you have to change, stop waiting for her miss and go for it'. That's what I did."

Belarus' Aryna Sabalenka serves the ball to Spain's Paula Badosa during during the women's singles match of the 2021 WTA Tournament Finals in Zapopan, Mexico, Nov 11, 2021. (ULISES RUIZ / AFP)

Earlier, Greece's Sakkari got an early service break to take a 2-1 lead and grabbed the first set when Swiatek sent a forehand into the net when returning a second serve.

Swiatek improved in the second set but Sakkari converted her third break point opportunity for a 4-3 lead that looked decisive given Sakkari's dominant serving.

ALSO READ: I felt I could do anything, says Swiatek, after cruising into third round

Iga Swiatek, of Poland, returns a shot to Maria Sakkari of Greece during the Mexican Tennis WTA Finals in Guadalajara, Mexico on Nov 11, 2021. (REFUGIO RUIZ / AP)

The Greek won 26 of 27 first serve points and was never broken in the contest played on the purple court in the high-altitude Mexican City.

Before match point, Swiatek appeared to start crying and after clinching victory Sakkari comforted her at the net with a hug.

Greece's Maria Sakkari (left) and Poland's Iga Swiatek greet at the end of the women's singles match of the 2021 WTA Tournament Finals in Zapopan, Mexico on Nov 11, 2021. (ULISES RUIZ / AFP)

"I saw that she was struggling. It wasn't a nice thing to see from the other side of the net," Sakkari said of her 20-year-old opponent, who won last year's French Open.

"She's a very, very nice girl. We always have great practices and great chats. It was something natural," she said of the hug.

Sakkari improved to 3-0 against Swiatek, with all of those wins coming this year.

READ MORE: Indian Wells: Svitolina survives onslaught, Swiatek reaches 4th round

The powerful Sakkari is enjoying a breakthrough year, having reached the semi-finals of the French Open and US Open to secure a career-high world ranking of number six.

Maria Sakkari of Greece reacts after winning a point against Iga Swiatek, of Poland, during the Mexican Tennis WTA Finals in Guadalajara, Mexico on Nov 11, 2021. (REFUGIO RUIZ / AP)

The WTA Finals divides the players into two groups of four to play in a round-robin format, with each player competing in three matches.

The top two from each group will advance to the semi-finals.

The WTA Finals were not held last year because of the COVID-19 pandemic.