So one-sided was the encounter, Nishikori broke serve four times and lost just six points when serving.
Tomic, the world number 53, never looked like gaining a foothold in the contest – particularly as he struggled to put any pressure on the Nishikori serve.
Awaiting Nishikori in the last four is Canadian third seed Milos Raonic, who found it tougher to advance on Friday.
Raonic won the battle of the big servers, overcoming Australian Sam Groth 7-6 (7-5) 3-6 7-6 (7-2) in two hours.
The duo combined for 37 aces – Raonic hit 15 of them – and just one break of serve, which went Groth's way in the second set.
Groth and Raonic served at 76 and 68 per cent respectively, and that was always going to make a straightforward result tough.
But Raonic got the better of the third-set tie-break to win through.
On the other side of the draw, Bulgarian fourth seed Grigor Dimitrov brushed past Slovakian left-hander Martin Klizan 6-3 6-4.
Dimitrov may have been rusty in his second-round win but he was much-improved against Klizan to advance.
He will likely face Swiss top seed Roger Federer, who faces Australian James Duckworth later on Friday.