Top-seeded Dominic Thiem reached the quarterfinals of the St. Petersburg Open with a 7-6 (4), 6-4 win over Jan-Lennard Struff on Thursday.

The Austrian player’s next opponent will be eighth-seeded Daniil Medvedev of Russia, who prevailed against Mikhail Kukushkin 6-3, 6-4.

Russian veteran Mikhail Youzhny retired from tennis after losing 7-6 (6), 3-6, 6-3 to fifth-seeded Roberto Bautista Agut of Spain.

Fabio Fognini of Italy returns the ball to Martin Klizan of Slovakia during the St. Petersburg Open ATP tennis tournament match in St.Petersburg, Russia, Wednesday, Sept. 19, 2018. (AP Photo/Dmitry Lovetsky)

The 36-year-old Youzhny won 10 tour titles and reached a career-high ranking of eighth in 2008.

Defending champion Damir Dzumhur of Bosnia progressed by beating Guido Pella 6-4, 6-4.

Dzumhur landed 70 percent of his first serves as he set up a meeting with Stan Wawrinka.

Mikhail Youzhny of Russia returns the ball to Mirza Basic of Bosnia and Herzegovina during the St. Petersburg Open ATP tennis tournament match in St.Petersburg, Russia, Wednesday, Sept. 19, 2018. (AP Photo/Dmitry Lovetsky)

Nineteen-year-old Canadian Denis Shapovalov defeated Matteo Berrettini of Italy 7-6 (6), 4-6, 6-0. He next plays Martin Klizan.

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Source: The Associated Press