Japanese No.1 Kei Nishikori is into the last 16 of the Australian Open for the sixth-straight year, dispatching third-round opponent Lucas Lacko in straight sets.

Nishikori hit 46 winners on Friday night in a 6-4 6-4 6-4 defeat of the Slovakian in two hours and 11 minutes.

The fifth seed said he was most pleased with his serving effort.

“There were a few tough moments, especially in the third set but I stayed tough and I’m very happy to win,” he said.

“I really did well with my service game … on some important points, I made a good first serve and that saved me a lot.

He moves on to a marquee fourth-round match-up with Roger Federer or Tomas Berdych.

“It’s going to be a tough next opponent. I’m feeling really good in my body – physically and mentally too – so I’ll try to relax before it.”