NEW YORK, Sept. 1 (UPI) --
Top-seeded world No. 1 Serena Williams
landed in the quarterfinals but third-seeded Agnieszka Radwanska
was an upset victim at the U.S. Open Sunday.
Williams needed only 87 minutes to get past the 15th-seeded fellow American Sloane Stephens 6-4, 6-1, firing six aces on her way to the fourth-round victory.
The defending champ has won four U.S. Open titles overall.
She now goes on to face No. 18 Carla Suarez Navarro following the Spaniard's surprising 4-6, 6-3, 7-6 (7-3) defeat of eighth-seeded Angelique Kerber of Germany Sunday.
The news wasn't as good for Poland's Radwanska, however, who was upended by 24th-seeded Russian Ekaterina Makarova 6-4, 6-4, keeping intact her record of never having reached the New York quarterfinals.
Makarova will next take on China's fifth-seeded Li Na, who brushed past former world No. 1 Jelena Jankovic 6-3, 6-0 in a 57-minute affair.
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