Top seed and former champion Tomas Berdych beat Dustin Brown of Germany 7-5, 6-3 to reach the quarterfinals of the Stockholm Open on Thursday.
The Czech, who had a bye into the second round, is coming off finals appearances in the last two weeks in Beijing and Shanghai.
He needs to reach the final here to stay in the running for a berth in the eight-man ATP Finals.
Next up for Berdych, the 2012 Stockholm champ, will be Marius Copil of Romania, who beat fellow qualifier Pierre-Hugues Herbert of France 6-4, 6-3.
Jack Sock of the U.S. put away sixth-seeded Jeremy Chardy of France 7-6 (3), 6-3 to line up defending champion Grigor Dimitrov in the quarterfinals, and qualifier Matthias Bachinger of Germany hit 15 aces as he upset fifth-seeded Leonardo Mayer of Argentina 7-6 (3), 6-7 (4), 6-3.
Fourth-seeded Alexandr Dolgopolov of Ukraine fell to a third straight loss in his comeback from a knee operation, in losing to Adrian Mannarino of France 6-4, 6-7 (2), 7-6 (4).