Karen Khachanov beat Kevin Anderson 6-3 7-6(5) at the Gread Ocean Road Open on Friday.
The 24-year-old Russian did not drop serve throughout the contest and secured the only break of the match midway through the opening set of the Australian Open warm-up event.
Khachanov next faces unseeded Dutchman Botic Van de Zandschulp, who upset American sixth seed Reilly Opelka in two tie-break sets.
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In other round of 16 matches, Italian teenager Jannik Sinner downed Aljaz Bedene 7-6(6) 6-2, while home favourite Jordan Thompson sailed past Spaniard Mario Vilella Martinez 6-4 6-4.
All quarter-final matches at the event will take place later on Friday. Play was suspended on Thursday when more than 500 players and officials were tested for COVID-19 after a worker at one of the quarantine hotels in Melbourne contracted the novel coronavirus.
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