Nishikori, the No. 4 seed, defeated Feliciano Lopez 7-6 (7-4), 6-0. After a tight first set in which both players had a pair of breaks, Nishikori won more than three-quarters of the points in the second set, finishing off three of his four break chances. Lopez won just eight points in the set.
No. 3-seeded Milos Raonic, who lost to Nishikori in the Japan Open final last year, also gained a spot in the quarters, taking out Jeremy Chardy 6-4, 6-3 without facing a break point. Raonic had 17 aces and lost a mere seven points in his 10 games serving.
Nishikori takes on Almagro in Friday's quarterfinals. They are in the same half of the draw as No. 1-seed Juan Martin del Potro and Alexandr Dolgopolov. Raonic goes against Lacko in the bottom half of the draw where Ivan Dodig and Jarkko Nieminen make up the other quarterfinal.
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