Having conceded early in their quarter final, Derry city came back to beat Cork City 2:1 after extra time at Turners Cross on Monday evening.
On nine minutes Mark O'Sullivan slotted home to put the hosts one up but before the break Ramelton's Barry McNamee brought the sides level.
With neither team able to add to the scoreboard extra time was required.
Five minutes into the first period of added time, Dean Jarvis headed home from Nathan Boyles cross to secures Kenny Shiels' men a place in the last four.
Shamrock Rovers and St Pats are also through, Rovers beat Shelbourne on penalties after a 1-all draw and St Pats beat Bray 3-0 at the Carlisle grounds.
The last quarter is tonight with Limerick hosting Galway United.