US Open 2016: Kei Nishikori tees up Andy Murray quarter-final with crushing win

Japan's finest was always likely to trouble the big-serving Karlovic if he could take the Croatian deep into rallies, and that is exactly what happened in-front of a packed Louis Armstrong Stadium at Flushing Meadows.

"It's never easy against someone like Ivo, he has a great serve," Nishikori said in an on-court interview. "I made a lot of returns of first and second serves and was happy with my return game today."

Nishikori will play either second seed Andy Murray of Britain or 22nd seed Grigor Dimitrov in the quarter-finals.

"I've been playing well, especially today," the Japanese said. "I think I played one of (my) best matches so far. So will try to recover well and play (more) good tennis next round."

Nishikori at his best is capable of sensational tennis and he made his fourth-round opponent work for every point, hitting a string of terrific winners - particularly in a barnstorming first set that was over and done with in just 25 minutes.

Karlovic made a better fist of the second set and produced his best tennis towards the end of the third and final set, forcing a tie break and then saving a string of match points.

But an unforced forehand error sealed the Croatian's fate, in a manner that has become all-too familiar in his frustrating career.

Nishikori's assured performance should see him full of confidence ahead of his second Grand Slam quarter-final of the season. But only once has he ever made it past the quarter-final stage of one of tennis' showpiece events, reaching the final of Flushing Meadows in 2014 where he lost to Marin Cilic.

He will now meet Murray, the reigning Wimbledon and Olympic champion, for a place in the semi-finals.