He will head in as favourite on Sunday against 16th-ranked Medvedev, although the 22-year-old put on a serving clinic of his own to press his title claims in a 7-6 (8-6) 6-2 defeat of French veteran Jo-Wilfried Tsonga.
Nishikori has set his sights on returning to the world's top five after falling to 39 last April due to a wrist injury at the end of 2017 that forced him to take a break from the tour.
"Great final today, I lost to him a year ago in the final in Japan, so I'm happy to get revenge today", Nishikori added.
Four-time champion David Ferrer broke Robin Haase six times en route to a 6-2 6-1 victory, while Leonardo Mayer ousted ninth seed Steve Johnson 7-5 6-3. "Tomorrow I will go for a trophy", Nishikori, the 2014 USA open finalist said after the win.
"I'm really happy that finally I've won this title, it's been like seven or eight times at this tournament", Nishikori said.
"I was a bit more aggressive than him and it made the difference", he said. He served out the set to level the match, 6-3.
Both players held serve through the first set, although the Russian player faced three set points in the 10th game, but he eventually lost the set in a tie break a couple of games later.
"Physically and tennis-wise I think it was flawless".
· Karolina Pliskova won her second Brisbane title, coming back from a set and 5-3 down in the second set to beat Lesia Tsurenko, 4-6, 7-5, 6-2.
"Maybe first match [against Denis Kudla] was a little bit tight, but after Dimi's [Grigor Dimitrov] match and today's match was nearly flawless, I would say".
"I'm continuously learning and that's something that's never going to change for me", he said. "Hopefully this isn't like a recurring thing".
"This helpless feeling I have, I think today I learned what I have to do to, not fix it, but what I can do to improve the situation so there aren't many moments that I feel like that", the Japanese added.