U.S. Open tennis: Sinner, Swiatek reach quarterfinals; Muchova upsets Paolini

Sept. 3 (UPI) -- Top-ranked Iga Swiatek and Jannik Sinner each used straight-sets victories to climb into the quarterfinals of the U.S. Open , while Karolina Muchova upset Jasmine Paolini on Day 8 of the tennis Grand Slam .

Muchova, the No. 52 player in the WTA Tour singles rankings, earned the first major victory Monday in Flushing, N.Y. The Czech tennis star needed just 69 minutes to dispatch her No. 5 foe.

"I think it was a very tricky, tough match," Muchova told reporters. "I was actually a little bit nervous. I don't know why. It was kind of a weird match. I had a weird feeling in my body the whole match, but I'm glad that I won."

Muchova edged Paolini 3-1 in aces and 17-10 in winners in her 6-3, 6-3 victory. She converted 4 of 7 break point opportunities, compared to 1 of 3 for the Italian, in the straight-sets win.

Muchova will meet No. 21 Beatriz Haddad Maia of Brazil in the quarterfinals. Haddad Maia ousted No. 71 Caroline Wozniacki of Denmark in a three-set thriller, which lasted two hours and 41 minutes at Louis Armstrong Stadium.

The Brazilian totaled five aces, 40 winners and converted 5 of 8 break point opportunities. Wozniacki totaled 23 winners and converted just 3 of 16 break point chances.

The winner of the Muchova-Haddad Maia match will face Swiatek or No. 6 Jessica Pegula of the United States in the semifinals. Pegula earned a victory in the early wave of Monday's matches.

She beat No. 18 Diana Shnaider of Russia 6-4, 6-2 in a fourth-round meeting that lasted 87 minutes at Arthur Ashe Stadium. Pegula edged Shnaider 6-1 in aces and 22-14 in winners. She also converted 5 of 10 break points. Shnaider converted 2 of 9 break point chances.

Pegula has never advanced to the semifinals, in a singles circuit, of a Grand Slam. She is set to make her seventh singles quarterfinal appearance at a major.

Swiatek, of Poland, needed just 90 minutes to beat No. 17 Liudmila Samsonova of Russia 6-4, 6-1. The women's No. 1 singles player totaled three aces, 14 winners and 19 unforced errors. She converted 3 of 8 break point chances. Samsonova totaled one ace, 11 winners and 24 unforced errors. She did not earn a break point opportunity.

On the men's side, No. 25 Jack Draper of the United Kingdom beat No. 39 Tomas Machac of the Czech Republic 6-3, 6-1, 6-2 to reach the quarterfinals.

Draper will compete with No. 10 Alex de Minaur of Australia in the quarterfinals. The winner of that match will face No. 1 Jannik Sinner of Italy or No. 5 Daniil Medvedev of Russia in the semifinals. De Minaur beat No. 32 Jordan Thompson, a fellow Australian, 6-0, 3-6, 6-3, 7-5 in a fourth-round match that lasted nearly 3 hours.

Thompson edged de Minaur 6-5 in aces and 34-31 in winners but logged 59 unforced errors, compared to 26 for his foe. De Minaur broke Thompson's serve seven times. Thompson converted 3 of 4 break point opportunities.

Sinner advanced to the quarterfinals with a 7-6(3), 7-6(5), 6-1 triumph over No. 14 Tommy Paul of the United States. Sinner edged the American 10-4 in aces. He totaled 33 unforced errors, compared to Paul's 43.

Medvedev advanced with a 6-0, 6-1, 6-3 triumph over No. 34 Nuno Borges of Portugal. Medvedev totaled nine aces, 21 winners and 20 unforced errors. He also converted 7 of 10 break point opportunities. Borges totaled five aces, 19 winners and 51 unforced errors. He converted 1 of 5 break point chances.

No. 12 Emma Navarro of the United States will meet No. 29 Paula Badosa of Spain in the first singles quarterfinal match of the day Tuesday in Flushing. The winner will meet No. 7 Zheng Qinwen of China or No. 2 Aryna Sabalenka of Belarus in the semifinals. Sabalenka and Zheng will meet in their quarterfinal match at 7 p.m. EDT Tuesday at Arthur Ashe Stadium.

No. 4 Alexander Zverev of Germany will face No. 12 Taylor Fritz of the United States in the first men's singles quarterfinal of Day 9. That match will start after the Badosa-Navarro meeting.

No. 20 Frances Tiafoe of the United States will face No. 9 Gregor Dimitrov of Bulgaria in another men's quarterfinal after the Zheng-Sabalenka meeting.

U.S. Open coverage will air from noon to 11 p.m. Tuesday on ESPN.