The top-seeded Nishikori posted a comeback 3-6, 6-3, 6-2 win over his Russian opponent in a 2-hour, 18-minute effort at the Racquet Club of Memphis.
Nishikori took last year's event in a championship match against Spain's Feliciano Lopez.
Also Friday, No. 4 seed Yen-Hsun Lu bested Alex Kuznetsov 6-1, 6-4.
His semifinal opponent will be Ivo Karlovic, who triumphed over American Jack Sock 7-6 (7-4), 6-7 (3-7), 6-3.
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