Nishikori looked to be racing into a quick one-set lead as he took the opening three games, breaking Raonic in the second.
However, the Canadian had other ideas and managed to claw his way back level, breaking the Japanese to make it 2-3 then wrapping up the leveller with a thunderous backhand down the line.
From there the first set went with serve until the tie-break, in which Raonic went into a 3-0 lead before a battling fight-back from Nishikori saw him take it the set 7-6(5).
In the second set, Raonic started the stronger, winning his first service game to 15 before Nishikori saved two break points to level.
Nishikori tried to hang on but was broken in the eighth game to go behind 3-5. On Raonic's serve, Nishikori battled to deuce, but the Canadian saw out the set to take it to a decider.
The final set was one-way traffic, as Nishikori steamrollered Raonic 6-0 to win the title in front of his adoring public.