A day of upsets continued at the Dubai Duty Free Tennis Championships on Wednesday, with Veronika Kudermetova shocking defending champion Garbiñe Muguruza, and Petra Kvitova knocking out No.1 seed Aryna Sabalenka.

Kudermetova cracks the code: Kudermetova of Russia earned her first win over Muguruza, upsetting the defending champion 3-6, 6-4, 6-4 to reach the quarterfinals.

The pair had contested three prior matches, with No.4 seed Muguruza of Spain winning each of those times. But on this occasion, Kudermetova at last notched victory over the former World No.1, taking the 2-hour and 17-minute clash to earn the seventh Top 10 win of her career.

It is the second straight win over a former World No.1 for 31st-ranked Kudermetova. The Russian knocked out former Dubai finalist Victoria Azarenka in the first round on Tuesday.

The victory continues a solid start to the season for 24-year-old Kudermetova, who reached the final of Melbourne Summer Set 1 (losing to Simona Halep) and the third round of the Australian Open in January.

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Meanwhile, World No.7 Muguruza's win-loss record for 2022 falls to 3-3. She and the woman she defeated in last year's Dubai final, Barbora Krejcikova, were upset nearly simultaneously on Wednesday.

More from Wednesday in Dubai: Ostapenko takes out Swiatek, Yastremska upsets Krejcikova

Muguruza's 68 percent first-serve percentage was not high enough on the day to overcome Kudermetova's success returning the Spaniard's second serve. Kudermetova won 58 percent of Muguruza's second-service points, while also prevailing on 62 percent of her own.

Key moments: Muguruza took charge down the stretch of the opening frame, collecting the one-set lead with a thunderous love hold punctuated with an ace.

However, Kudermetova was more precise on serve in the second set, facing and saving a single break point. The Russian was rewarded for her cleaner play with the lone break of the set at 5-4, which she collected with a stirring forecourt winner at the end of a dizzying rally.

An up-for-grabs decider saw each player hold with ease until 4-4, where Kudermetova fended off two break points before closing out the game with another bold putaway.

Once more, Kudermetova was recompensed for her effort in the next game. After an ace gave Muguruza game point, the defending champion suddenly hit three consecutive double faults, ceding the break, and the match, to Kudermetova.

Next up: Kudermetova will take on Swiss lucky loser Jil Teichmann in the quarterfinals. Teichmann, ranked World No.35, bested two-time Dubai champion Elina Svitolina earlier on Wednesday. Kudermetova has won both of her previous meetings with Teichmann.

Kvitova stops Sabalenka

Kvitova, the Dubai champion in 2013 and runner-up in 2019, jumpstarted her season with victory over World No.2 Sabalenka of Belarus, 6-4, 6-4 in an hour and 25 minutes. Kvitova is now 3-2 against Sabalenka.

Former World No.2 Kvitova of the Czech Republic was just 2-4 in 2022 coming into Dubai, and her ranking has slid to World No.25. But the two-time Wimbledon champion pulled off her 11th career win over a Top 2 opponent to reach her first quarterfinal of the season.

Among active players, only Serena Williams (47), Venus Williams (28), Kim Clijsters (12) and Svetlana Kuznetsova (12) have more wins over Top 2 players than Kvitova.

Kvitova's success on service points overall was marginally better than Sabalenka; Kvitova claimed 74 percent of points behind her first serve while Sabalenka won 66 percent. But Kvitova was sturdier when she had break points, converting four of eight while Sabalenka went 2-for-5.

Sabalenka steered back from an early break down in the first set, but Kvitova regained control of the opening frame with a break for 4-3. Serving for the set at 5-4, Kvitova slammed massive serves to reach triple set point, then converted the third of those chances with an error-forcing backhand.

It was Kvitova's turn to come back from a break down in the second set, easing to the win from there. Once again, Kvitova got her critical break in the 3-3 game, and the power game sealed victory, with winners from both wings aplenty.

In the quarterfinals, Kvitova will take on Jelena Ostapenko of Latvia, who upset No.6 seed Iga Swiatek on Wednesday. Kvitova has a slim 4-3 lead in her rivalry with 2017 Roland Garros champion Ostapenko.