The 28-year-old American, who has dropped to 73 in the world following first-round exits in his previous two tournament, was hardly troubled as he extended his winning run at the hardcourt event to seven matches.
Fish will next play fourth seed Jeremy Chardy, who was taken to three sets by Colombian Santiago Giraldo 7-5 6-4 7-5, and the American is looking forward to the last-eight clash.
"You've got to serve well against him," Fish said.
"He's a great player, plays well on all surfaces. There's potential for both of us to win, for sure. I feel like I have a little bit of an edge out here just winning seven matches in a row here, and I'll take that confidence."
Big-serving second seed Ivo Karlovic fended two tie-breaks to fend off Germany's Daniel Brands 7-6 (10/8) 7-6 (8/6) in a match during which neither player was able to break serve.
Karlovic will meet veteran American James Blake in the quarter-finals after the seventh seed breezed past Robin Haase 6-3 6-1.
Benjamin Becker, the third seed, was handed a free pass into the quarter-finals affter Wayne Odesnik withdrew from their match with an ankle injury.
Becker will next meet Finn Jarkko Nieminen who battled back from a set down against fifth seed Evgeny Korolev 5-7 6-1 6-0.
Latvia's Ernests Gulbis fired five aces in his 6-1 6-4 win over Teimuraz Gabashvili and will meet Leonardo Mayer, who won yesterday, in the last-eight.