Long put Dave O’Keeffe’s side in front in the 15th minute with a 25 yard strike that flew into the top of Paul Drummond’s net.
In a half that Avondale dominated, Corinthians found themselves level two minutes before the break when Hugh O’Donovan nudged over Peter Moreland in the box and Moreland dispatched his spot kick.
The holders were back in front six minutes into the second-half when Eoin Lougheed picked Long out with an inch perfect first time cross and the striker’s diving header gave the excellent Drummond no chance.
Corinthians were then handed a lifeline when Michael Mulconry brought Kevin Madden down in the box but Daniel O’Leary made a great stop low to his right to deny Moreland. Ray Lally made sure of the win six minutes from time with another excellent long range strike.
Crumlin United looked to be strolling through to the last 16 as they went 4-0 up against visitors Cobh Wanderers but the Cobh side fought their way back to give Crumlin a late scare before eventually bowing out 4-3.
St Mary’s booked their quarter-final spot with a 1-0 win over Killester at St Mary’s Park, while UCC had to come from behind to force a replay with Glenville as the sides drew 1-1 at The Farm.
Casement Celtic will fancy their chances of making home advantage count in their replay with Edenderry Town after the team’s 1-1 drew in Offaly, while Firhouse Clover defeated Arklow Town 1-0 in Arklow on Friday night.
In the other two games, high-flying Tolka Rovers hammered Dunboyne AFC 6-1 in Meath, while St Mochta’s are through after a 2-1 home win over Cockhill Celtic.
Meanwhile, there were two games in the Munster Senior League Premier Division on Friday night, where Rockmount defeated Douglas Hall 2-1 at Moneygourney, while Carrigaline United saw off Midleton by the same scoreline at Knockgriffin.
In the first division, Blarney United maintained their eight point lead at the top after drawing with second placed Bandon 1-1 in Bandon, where Aidan O’Donoghue scored for the home side, with Patrick Crowley on the mark for the leaders. In the other first division match played, Mayfield United defeated Ringmahon Rangers 2-1 at Ringmahon Park.
In the Munster Senior Cup quarter-final, Limerick FC defeated Leeds 3-1 in Kilmallock with goals from Dean Clarke (2) and Sean Russell.
Meanwhile, Cork City got their pre-season preparations off to a winning start with a 1-0 victory over PSC Soccer Academy at O’Shea Park in Blarney yesterday.
New signing Karl Sheppard headed home the only goal early in the second-half, in a game where the other big signings Kieran Djilali and Gavan Holahan also started.