Willo McDonagh (left) and Killian Brennan both scored

Killian Brennan put Derry ahead in the 16th minute but the home side missed other first-half chances with Ruaidhri Higgins hitting the woodwork.

However, BJ McMcMenamin levelled on 54 minutes and Willo McDonagh hammered in a superb winner on 87 minutes.

Derry must beat Drogheda by two goals in their next game to make the semis.

Glens started without eight regulars including Gary Hamilton, Michael Halliday, Elliott Morris and the suspended Jason Hill.

For the most part, Derry dominated in the first half and Glens goalkeeper Michael Dougherty had to make two good early saves to deny Kevin McHugh.

At the other end, Pat Jennings made a smart save to stop a Chris Morgan effort but Derry were bossing the game and it was little surprise when they took the lead on 16 minutes.

The Glens defence was slow to clear after the ball had been delivered into the box and Brennan hammered the ball home from 10 yards.

Derry had chances to add to their lead with the best effort Ruaidhri Higgins' drive on to the woodwork with Barry Molloy heading the rebound wide.

Pat Fenlon shouts as things again go wrong at the Brandywell

Such was Derry's dominance that they should probably have been further ahead at the interval and there was a suspicion that they could be made to pay later in the game.

So it proved in the 54th minute with McMenamin grabbing the chance to impress by striking Glentoran's equaliser.

Derry attempted to regroup and McHugh had a chance within three minutes but he failed to make a connection and the ball was cleared.

Derry had already lost centre-half Darren Kelly to injury and they suffered a further blow when their other central defender Ken Oman was stretchered off midway through the second half.

Oman later came back on to the field but it was obvious that he was far from 100 per cent fit.

Sensing their chance to regain some pride after their early exit from the competition, Glentoran pressed for the winner and it came three minutes from time when McDonagh hammered in a glorious strike from all over 22 yards.

It was another bad blow for Derry boss Pat Fenlon, who already looks somewhat beleaguered despite only being in the Brandywell job for less than four months.

Derry have lost four of their last five league games and their season is threatening to unravel scarcely before it has begun.