As the highest remaining seed in a high-quality draw in Brisbane after world No2 Rafael Nadal pulled out, Nishikori beat world No16, Daniil Medvedev, one of the brightest young prospects on the tennis scene, in a seesawing two hours, 6-4, 3-6, 6-2.
The 29-year-old Japanese star was in superb form as he put on a commanding all-court display against his French opponent to advance to the final for the second time in three years 6-2 6-2.
"I was really nervous and he started awesome", Medvedev said.
"Rennae said 'I am absolutely sure you can win this match, ' which gave me some confidence and belief that I can do it. But then the ball wouldn't go in, and then I would go back to being like childish and stuff", Osaka said.
"I managed to come back in the second set, but he played awesome and deserved it", Medvedev said of Nishikori.
"Despite (the) many chances that he had, I managed to hold my serves so I'm happy about it and I'm happy about the win", he said.
Nishikori was all over the Russian in the second set, his powerful and well-directed groundstrokes forcing Medvedev into errors.
Nishikori also moved around the court well, his speed not noticeably affected by the injuries that hampered him previous year. With world No5 Juan Martin del Potro already announcing his withdrawal from the first Major of the year, that guarantees Nishikori one of the top eight seedings, a level that means he can not meet a higher-ranked man before the quarter-finals. "I feel like I didn't really know how to cope with not playing well".
"Physically and tennis-wise I think it was flawless". Pliskova won her first Brisbane title two years ago.
Medvedev, who beat Nishikori in the 2018 Tokyo final, was bidding for a 4th career title.
Last year's finalist Nishikori, who prevailed 6-4 3-6 6-2, won 70 percent of points on his first serve and converted five out of 15 break point opportunities to snap a nine-match losing streak in finals.
"It was hurting a little bit, but I said, "just fight till the end".