The 24-year-old on Wednesday became the first Japanese man since 1918 to make the semi-finals in New York.
But Chang, himself a Grand Slam title winner at the 1989 French Open, told the 10th seed that his work is not completed following his epic 3-6, 7-5, 7-6 (9/7), 6-7 (5/7), 6-4 quarter-final win over Australian Open champion Stan Wawrinka.
"He's telling me to stay focused in the match and never get frustrated too much and always pump up yourself," said Nishikori of the man he has worked with since January this year.
"He told me congrats on winning this battle. But he also says it's not done. Stay focused and try to recover these two days, and hopefully have another good one next one,” he added.
Nishikori triumphed over third-seeded Wawrinka in 4 hours 15 minutes, his second marathon clash after needing 4 hours 19 minutes to get past Milos Raonic in the previous round – a match that started on Monday and ended at a record-equalling 2:26am on Tuesday.
Nishikori will face either world number one Novak Djokovic or Andy Murray, both former champions, on Saturday for a place in Monday's championship match.
The Florida-based player admitted it had been a strange few days following his Raonic marathon.
"I slept at 6:00 a.m. That was a little bit tough because I never had that experience. I had a little bit of jet lag today, but my body is good,” he said.
He even said he was happy to keep playing five-set matches, and with his ability to go the distance he has exceeded his best previous performance at a major, a run to the Australian Open quarter-finals in 2012.
His record in five-set matches is now nine wins against two defeats.
"I always love to play five sets. I think I have a good record. I have a lot of confidence to play in the fifth. I get more concentration and my tennis is better in the fourth or fifth sets,” he said.

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