Nishikori hit 22 winners and held his serve to win the second-round match on the outdoor clay court in one hour, eight minutes.
Nishikori took control of the match by hitting 11 winners and breaking Gabashvili before finishing out the first set by holding his final serve to love.
Gabashvili tossed his racket down after a third double fault cost him his service as he fell behind 3-2 in the second set. Nishikori then struck an ace to finish the match.
"It was a great first match," Nishikori said. "It was my first match of the year on clay, so I was little tight, but I played a great two sets today."
Earlier, Russian teenager Andrey Rublev beat former champion Fernando Verdasco 7-6 (4), 6-3 in the first round.
The 17-year-old Rublev, who entered as a qualifier ranked 329th, broke the Spaniard three times while saving five break chances. Rublev will next face 13th-seeded Fabio Fognini.
Albert Montanes came back to defeat Ricardas Berankis 1-6, 6-4, 7-5 and will meet David Ferrer in the second round, where 2014 U.S. Open winner Marin Cilic will play Victor Estrella after Estrella ousted Dominic Thiem 6-3, 7-6 (3).