Reilly Opelka recorded 11 aces while notching a 2-6, 7-5, 6-4 upset of top-seeded Russian Daniil Medvedev on Thursday to reach the quarterfinals at the St. Petersburg Open in Russia.
The 6-foot-11 American recovered from a shaky first set to record an upset of the defending champion in the hardcourt event. Opelka's quarterfinal opponent will be seventh-seeded Croatian Borna Coric, who cruised to a 6-3, 7-5 win over Russian wild card Roman Safiullin.
Second-seeded Canadian Denis Shapovalov rolled to a 6-1, 6-4 win over qualifier Ilya Ivashka of Belarus and third-seeded Russian Andrey Rublev fought to a 4-6, 6-4, 7-5 victory over France's Ugo Humbert. No. 4 Karen Khachanov posted a 4-6, 7-5, 6-3 win over wild card and fellow Russian Aslan Karatsev and No. 6 Milos Raonic of Canada rolled to a 6-3, 6-2 triumph over Alexander Bublik of Kazakhstan.
Top-seeded Alexander Zverev recorded seven aces and won 84.2 percent of his service points while rolling past Spain's Fernando Verdasco 6-4, 6-1 in a second-round match at Cologne, Germany.
The German needed just 63 minutes to finish off Verdasco and reach the quarterfinals. Zverev will next face South Africa's Lloyd Harris, who defeated American Steve Johnson on Wednesday, 7-6 (5), 7-6 (2).
Also, second-seeded Roberto Bautista Agut of Spain recorded a 6-4, 7-6 (5) victory over Gilles Simon of France; third-seeded Canadian Felix Auger-Aliassime was a 6-4, 6-1 winner over Swiss qualifier Henri Laaksonen; and Spain's Alejandro Davidovich Fokina registered a 3-6, 7-6 (3), 6-2 upset of eighth-seeded Marin Cilic of Croatia.
Forte Village Sardegna Open
Germany's Yannick Hanfmann dominated third-seeded Casper Ruud of Norway 6-2, 6-1 to advance to the quarterfinals at Santa Margherita di Pula, Sardinia.
Hanfmann will next face Lorenzo Musetti, who rolled to a 6-2, 6-1 victory over fellow Italian Andrea Pellegrino. The 18-year-old Musetti needed just 60 minutes to complete the sweep.
Fourth-seeded Albert Ramos-Vinolas of Spain notched a 6-0, 6-3 win over Corentin Moutet of France, while Italy's Marco Cecchinato defeated American Tommy Paul 7-6 (1) 6-4.
--Field Level Media