The defending Tokyo champion will meet either Britain's Andy Murray [ Images ] or Davis Cup team mate David Ferrer in the final on Sunday after winning in just over an hour and a half.
Nadal predictably cranked up the pressure at 5-5 in the first set, a bullet return forcing the break as fourth seed Fish dumped a backhand into the net.
The Spaniard, playing his first tournament since helping his country reach the Davis Cup final last month, toyed with Fish in the second.
Nadal raced to a 4-0 lead in brilliant sunshine and a tormented Fish slammed his racquet to the court in frustration after going 5-1 down.
The end came swiftly for Fish, Nadal teeing up match point with an astonishing running forehand down the line to underline the gulf in class between the players.
The final point summed up Fish's day, the American embarrassingly framing an attempted Pete Sampras-style leaping smash into the bottom of the net after a decent first serve.