A master of technique, Cunningham exposed lack of concentration by the Northern defence, and with minimum backlift chipped a top-spinning shot past keeper Nick Grant to clinch the cup result after 75 minutes.
Cunningham ruled the roost in central midfield for Roslyn, spreading calm, stroking passes, and, like all good players, he always appeared to have time to spare.
Roslyn made an impact start by scoring in the opening minutes when Sam Mepham was fed by Mike Still, and hit a cheeky lob that exposed the Northen defence and had the home support cheering at 1-0.
But even the Roslyn faithful remembered that Northern won the last league encounter, and predictably coach Steve Brook's side dug deep and launched attacks mainly through the pace and aggression of Dave Henderson.
In contrasting style, Roslyn stroked passes around, looking for the killer pass, while Northern closed ranks and looked for an early ball forward to gain advantage.
Northern's cause was not helped when central defender Arran Wilkinson was elbowed in the eye, and, gushing blood, played no further part in the game.
Roslyn's passing strength radiated from Cunningham, and his younger, more mobile brother, Aajay, helped by more calm control from deep defender Tim Mather.
Both sides went on to hit the opposition crossbar, and in his last local game before leaving for Scotland, referee Hamish Phillip kept good control of the cup tie which generated many abrasive tackles.
Northern's best chance fell to Mike Arnold, who broke through but shot tamely into the arms of Roslyn keeper Peter Evans.
Roslyn created more chances.
Sam Mepham launched shots and headers, Aajay Cunningham also tested the Northern keeper as did Fraser Cameron and Tom Connor.
As time ran out, Northern looked capable of forcing extra time, but Mike Cunningham's maestro goal over the wall clinched the tie and Roslyn continued to use its superior ball possession to play out time to the finish.
In other cup matches, Northern Hearts ran Dunedin Technical close before losing 2-1 in Timaru, while Caversham swamped Southend United 4-0 in Invercargill with goals by Ant Hancock, Anton Ross, Pat Fleming and Mike Jones.
Almost the shock result of the day was Grants Braes forcing University into extra time when it was 1-1 after 90 minutes, but the students had too much stamina and eventually won 5-1.
