The third-ranked Murray, who finished the match with the roof closed at Ariake Colosseum because of rain, lost only two points in the first five games and even threw in a few drop shots.
The U.S. Open champion and Olympic gold medallist broke Lacko in the third and seventh games of the second set and closed out the match on serve.
"Once I got the break in the second set, I started to play better," Murray said. "I have a couple of days until the next match, so hopefully I can stay in a good rhythm."
Seventh-seeded Stanislas Wawrinka of Switzerland also advanced to the quarterfinals, beating Jeremy Chardy of France 7-6 (1), 6-7 (6), 7-5. Chardy saved three match points in the second-set tiebreaker, but was broken in the 11th game of the final set.
Murray and Wawrinka will meet in the quarterfinals.
"I have had a lot of tough matches with him over the years," Murray said. "He is a good player, especially on the hard court."
Also, third-seeded Janko Tipsarevic of Serbia rallied to beat Gilles Simon of France 4-6, 6-3, 6-1 in the first round, and fourth-seeded Juan Monaco of Argentina defeated Bulgarian qualifier Grigor Dimitrov 6-2, 6-1.
Tipsarevic, ranked ninth in the world, was broken twice in the opening set but bounced back to eliminate the unseeded Simon.