“We have never met in a Grand Slam final. I have tremendous respect for him as a person and a player. He’s a great guy,” said Djokovic who missed the 2017 tournament through injury.
“He’s had lots of injury problems in the past but he’s a big-match player.”
Wimbledon champion Djokovic, playing in his 11th US Open semi-final, claimed a 15th win in 17 clashes against Nishikori.
It was plain sailing for the 31-year-old Serb who is chasing a 14th Slam title to take him level with Pete Sampras on the all-time list.
He broke serve four times while an under-par Nishikori saved 13 of the 17 break points he faced and committed 51 unforced errors.
Nishikori runs out of gas
Nishikori stumbled into a buzzsaw in the shape of Djokovic on Friday, but the Japanese star leaves the US Open pleased with a semi-final run one year after missing the tournament through injury.
“It was very good,” he said of his two weeks in Flushing Meadows. “Maybe not today, but the last couple of matches I played great tennis, beat a couple of good guys.
“I’m really happy to be in the semis again. Could have been better playing the final again, but maybe the my next chance.”
Nishikori made history in reaching the 2014 US Open final, but said he could hardly bring himself to watch last year’s tournament as he battled a wrist injury that brought his 2017 season to a premature close.
He has slowly made his way back in 2018, gradually gaining confidence with a quarter-final run at Wimbledon and his last-four appearance here.
He dug deep for a five-set victory over Marin seventh-seeded Cilic in the quarter-finals, and may have still been feeling the effects against Djokovic.
“I think I was just tired from the last couple of matches,” he said after his 6-3, 6-4, 6-2 defeat to Djokovic.
“I tried to give 100 percent but he was playing very solid.
“Maybe if he wasn’t Novak I might have had a chance, but he was playing great tennis today. Serve, return, groundstrokes — he was playing aggressive and I didn’t have much energy to stay with him.”