Golden boot leader Emiliano Tade increased his season tally to 14 with a late first-half penalty. Waitakere's first half went from bad to worse when All White Jake Butler was given his marching orders for a crude tackle on John Irving just before the break.
Tade then found the back of the net again with a low drive in the 48th minute.
The visitors made a raft of changes from the side that lost 4-0 the previous weekend, with imports Jordon Lowdon and top scorer Richard Cardozo on the bench and former All White Chad Coombes left out entirely.
Cardozo came off the bench in the second half to pull back a consolation goal with a classy finish before Robinson held out a flurry of late Auckland attacks.
The pacey Auckland attack trio of Tade, Ryan De Vries and Portuguese signing Joao Moreira caused Waitakere all sorts of problems, while defenders Ivan Vicelich and Angel Berlanga were rarely troubled by a blunt Waitakere front line.
Auckland will meet Wellington in the final at 2.35pm on Sunday at Kiwitea St.