Japan's Nishikori prevailed after three and a half hours on a baking Hisense Arena, recovering from an early wobble against his Russian opponent that vindicated his call to withdraw from an exhibition event last week to rest a hip injury.
"It was a little bit of a slow start today. I didn't quite play great tennis in the beginning, but especially in the fifth set I think I was really focused and played good tennis," Nishikori told reporters.
"I think he played well from the beginning. Yeah, it was tough, really tough match. "The 27-year-old, who needed medical treatment late in the fifth set, had an encouraging start to the year when he reached the final of a Brisbane warm-up, where he lost to Bulgaria's Grigor Dimitrov.
On Monday, Nishikori drove Kuznetsov, 25, all over the court in the second and third sets, a devastating forehand pass in the fourth game of the second set highlighting precision that the Russian could not match.
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As the temperature rose so too did the intensity of the contest, with Kuznetsov making the fifth seed fight for every point.
Nishikori won almost double the number of rallies consisting of nine or more shots, and about 20 percent more of the shorter rallies.
"It was unfortunate to play five sets in a long match," he said. "I'll try not to let it happen again, to play a long match like this. But, the... fifth set was pretty good, so I think I'm in good shape for the next round."
Nishikori, who has long carried Asia's hopes of a first male grand slam champion, will next play Frenchman Jeremy Chardy after the world number 72 eased into the second round when Spain's Nicolas Almagro pulled out with an injury.
(Editing by John O'Brien/Peter Rutherford)
