Glentoran manager Eddie Patterson accused his side of complacency as Championship 1 strugglers Bangor rocked the odds-on favourites with two goals in the first 11 minutes, but was delighted by his side's repsonse as they booked a quarter final trip to Knockbreda, with some comfort.
Patterson said: "I wasn't too happy with the way we started the game. We were too complacent with players believing that just because they were wearing Glentoran shirts they had a divine right to go through the next round.
"But they got a wake-up call when Bangor slammed in two well-taken goals and, to their credit, they moved up a couple of gears and hit three goals in the space of 10 minutes. We sealed our passage with two goals in the second half, and we are delighted to be in the quarter-finals."
Opposite number Garth Scates was encouraged by his side's performance which, he said, augers well for the rest of their league campaign.
"We got off to a great start, scoring two well worked goals, but then failed to defend at set pieces and gave away three goals.
"However we re-grouped, but then conceded a fourth goal at the start of the second half, and the match was all over," admitted Scates.
"The big plus for me is that I know that if we can perform at the level we did today against a top team, we will retain our place in Championship 1. So, we can take a lot of positives from today's game."
Bangor got off the mark after just two minutes 18 seconds. Midfielder Thomas Lambe got on the end of a pin-point Andy Morrow cross from the right to send a rocket header from eight yards past Glens keeper Elliott Morris.
Nine minutes later the Seasiders were two up. A slick four-man move saw the ball travel from Andy Hall on the right to Mark Cooling and then on to Ryan Mann who slipped the ball inside for striker Michael Doran to fire home from 12 yards.
The Glens took only three minutes to get back in the contest when a slip by the home rearguard allowed Stephen Carson to play the ball through for Andy Waterworth to make no mistake from 14 yards.
Four minutes later the scores were level when Jimmy Callacher notched his sixth goal of the season with a glancing five yards header from Stephen Carson's free kick on the right.
The Glens were now buzzing and on 24 minutes, following another Carson free kick on the right, Colin Nixon made it 3-2 as the visitors' skipper headed in via the underside of the crossbar. Referee Arnold Hunter pointed to the centre circle, ignoring the home team's protests that the ball had not crossed the line.
Four minutes after the break Richard Clarke was the provider for Marcus Kane to smash a 30 yards drive into the top left hand corner and the Glens completed the scoring on 82 minutes with a point blank David Howland header from Carson's inswinging corner from the left.