The third-seeded Opelka, who had a first-round bye, broke Nishioka’s serve in the final game of each set to earn his quarterfinal spot. He had dropped both matches on tour this season, blowing a two-set lead against Fabio Fognini in the Australian Open in the most recent one, and was on a five-match losing streak dating to October.
Opelka won his first career title last year on Long Island. He advanced to face Jason Jung, who upset No. 7 seed Cameron Norrie 6-4, 6-4 to reach the quarterfinals for the second straight year.