The fifth seed made it to the last 16 for the sixth straight year with a 6-4, 6-4, 6-4 victory over the Slovak qualifier in two hours, 11 minutes.

Nishikori will next face his first big challenge against either 17-time Grand Slam champion Roger Federer or big-serving Czech 10th seed Tomas Berdych.

The Japanese is looking to improve on his three quarter-final appearances at the Australian Open, losing to Andy Murray in 2012, Stan Wawrinka in 2015 and Novak Djokovic last year.

"There were some little tough moments, but I stayed tough in the third set," Nishikori said.

Nishikori broke the 121st-ranked Lacko's serve four times and gave up his own service only once.

"I did well with my service games and came up with some important first serves on the big points," he said.

"I am feeling well physically and mentally and I've been playing well in my three matches in Melbourne."

Nishikori got the early advantage with a service break in the seventh game after Lacko overhit a forehand.

The Japanese star got a double break to lead 3-0 and Lacko got one break back to trail 3-5 before Nishikori served out for a two sets to love advantage.

Nishikori peeled off a ripping forehand return winner to grab an early break in the final set to hit the front and stay there.

He hit 46 winners, 27 of them on his forehand, and dominated the rallies.

Nishikori became the first Asian man to contest a Grand Slam final when he lost to Marin Cilic at the 2014 US Open after defeating three top-10 players -- Milos Raonic, Wawrinka and Djokovic along the way.