Anastasija Sevastova, seeded 16th in the tournament, ousted 2006 champion Maria Sharapova, 5-7, 6-4, 6-2, to punch her ticket into the quarterfinal of the US Open Saturday. Sevastova hit 21 winners and committed just 14 unforced errors as she defeated Sharapova in two hours and 16 minutes. Sharapova, for her part, tallied 42 winners with 51 errors, 18 coming in the final set. In 2011, Sevastova was a Top 40 player in the WTA Tour but decided to take a brief retirement due to injuries and illnesses. She came back last year and made it to the last eight at Flushing Meadows after beating Garbiñe Muguruza and Johanna Konta.

The fourth-round finish for Sharapova came after she was suspended for 15 months due to use of banned substances. In her first major tournament since returning to the WTA Tour, Sharapova stunned No. 2 Simona Halep in the opening round and defeated Timea Babos and Russian-American teenager Sofia Kenin in the second and third rounds, respectively.

Sharapova, a former world No. 1, got off to a hot start as she took a 4-1 lead and never looked back from there, taking the opening set by hitting 18 winners. However, Sharapova unraveled in the second set, committing 16 unforced errors, allowing her opponent to take it via a score of 6-4. In the third, Sevastova rode the momentum of her victory in the second set, earning two early breaks.

Sharapova proved to be one tough customer to close out for Sevastova, who lost three match points, but clinched the win on the fourth one.

Stephens edged Julia Goerges

Next up for Sevastova is Sloane Stephens, who defeated No. 30 seed Julia Goerges of Germany in three sets, 6-3, 3-6, 6-1, to reach her first career US Open quarterfinal.

"I'm just really happy," said Stephens, who clinched the win after one hour and 41 minutes of play. Stephens and Sevastova will play each other for the first time.

Madison Keys ousted Elena Vesnina

Madison Keys, seeded 15th in the event, reached the Round of 16 after beating reigning BNP Paribas Open champion Elena Vesnina, , 2-6, 6-4, 6-1, in a match that finished almost 2 a.m.

Sunday. Keys will next face No. 4 seed Elina Svitolina for a spot in the quarterfinals. The match is crucial for Svitolina as she is one of four women who are vying for the No. 1 spot. "It's going to be really difficult. She's obviously had a phenomenal year,” Keys said of Svitolina. Earlier, world No. 1 Karolina Pliskova survived a tough challenge from No. 27 Shuai Zhang before escaping with a 3-6, 7-5, 6-4 win in the third round.

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