Hibs ran out comfortable winners with Derek Riordan and Jonatan Johansson also on the scoresheet against the Irn-Bru First Division side.
Kick-off at East End Park was delayed by 15 minutes as latecomers caused difficulties at the turnstiles, with a crowd of just over 4,000 watching the clash.
Nish slotted home the opener after just seven minutes, before chipping goalkeeper Greg Fleming for his second of the day after 33 minutes.
Any hope of a comeback from the Pars was shattered when Riordan rifled home from close range 10 minutes after the break.
Johansson – who had replaced Nish at half-time – then sealed the win in injury time after being set up for the strike by new signing Patrick Cregg.