Asia’s top player – who reached the semi-finals in Miami last year – was delighted with his display as he move into the last 16.
“I played good tennis today, almost perfect. I’m excited that I’m playing good here. Maybe he was hurting a little bit, but still I was giving him a lot of pressure with my return,” Nishikori said.
“It was a great match today. I felt great on the court, so very happy to win.”
Nishikori, 25, sent down five aces and 16 winners, breaking 39th-ranked Troicki on five of six chances in a dominant performance.
Nishikori, who reached his first Grand Slam final last year at the US Open, beat David Ferrer and Roger Federer on his way to the Miami semi-finals last year only to withdraw prior to a match with Novak Djokovic due to a groin injury.
“It was really sad last year, but I had a great year last year,” Nishikori said. “One of the keys was that I got a lot of confidence from the Roger win.”
Nishikori cannot repeat that since Federer is not playing at Miami this year, but he will next face Belgium’s David Goffin, who beat Poland’s Jerzy Janowicz 6-4, 6-3.
Elsewhere, world No 5 Milos Raonic hit 20 aces and edged No 31 Jeremy Chardy 6-1, 5-7, 7-6 (3).
Alexandr Dolgopolov of Ukraine also reached the fourth round with a 7-5, 6-4 win over Brazil’s Thomaz Bellucci.