The four-time defending champion needed little more than an hour to see off his opponent 6-1 6-1, setting up a showdown with world number one rival Andy Murray at the O2 Arena.
Djokovic got off to a flying start in the match, with two early breaks allowing him to race into a 4-0 lead in the opener.
Nishikori stopped the rot with a break of his own to finally get on the board, but the world number five was unable to hold his own serve immediately after as Djokovic moved within one game of the set.
The Serb successfully saw it out too, although he needed three set points and to save two break points to wrap up the opener.
Djokovic made even shorter work of the second set, once again storming into a 4-0 lead before Nishikori was finally able to get on the board with his first hold of the match.
It proved to be his only hold of the match too, as Djokovic broke again in the final game to take the second set in just 31 minutes and set up a final with Murray tomorrow that will determine not only the tournament winner, but also who ends the year as world number one. body check tags ::