Michael Halliday left the subs bench in the 64th minute to turn this game in Glentoran’s favour with a sublime glancing header.
The Oval favourite was only on the pitch six minutes when he made the most of Jason Hill’s inviting cross.
His typical strike levelled the match at 1-1, wiping out Glenavon’s 11th minute advantage when Tony Grant rose majestically at the back post to thump home a header from Hugh Davey’s cross.
It was just the impetus the Glens needed to go on and win a crucial three points which eases them back to the top of the Carling Premiership alongside Cliftonville on 50 points.
Jason Hill made it 2-1 with a rasping 73rd minute volley which took a deflection off the hapless Mark Haughey and Gary Hamilton completed the comeback eight minutes from time.
The big talking point at the end, however, was referee Brian Turkington’s (inset) decision to send off three players.
Glenavon duo Ryan Harpur and Hugh Davey both walked as did Glentoran’s Shane McCabe.
Harpur and McCabe were first to go just on the half-hour following a midfield clash and Davey saw red 13 minutes from the end with the Glens 2-1 in front.
And he was not long gone when Hamilton slotted home a third after the usually reliable Jay Magee failed to cut out a long diagonal pass leaving Keith Gillespie to gift wrap the chance.
Until Harpur walked Glenavon were not only in the lead but playing well. But afterwards they pulled debutant striker Rory Hamill into midfield to plug the gap and lost the early initiative.
Glentoran had to chase the game so stuck to their guns with two up front and it eventually paid off.
But it was the red cards which rankled and home boss Marty Quinn rapped: “I’m very concerned about the local game.
“I think a yellow card would have been suffice for Harpur and McCabe while Davey went for virtually nothing.
“There was a total misunderstanding between linesman and referee.
“Every week we’re getting three, four or even five players sent off. What has changed? Are players becoming more vigorous? I don’t think so.
“It’s zero tolerance now. Basically you cannot make a challenge. Players genuinely go in to play the ball. If they are a split second late it’s a yellow card.
“I think there needs to be more common sense. Look sideways and it’s a yellow card.”
Rival boss Alan McDonald said: “I think everybody shares the same concern. We’ve had two players red carded in the last two weeks.
“In my opinion they were not red card offences.
“At the end of the day we have our opinions as managers and coaches but on the field referees are the law and the judge.
“We have to trust they make the right decisions for the right offences.
“In my opinion there is a discrepancy in consistency. We’ve been talking to referees about it for the last two seasons.
“Hopefully somewhere along the line we can get some consistency from week to week.”
Despite defeat Quinn insisted: “We put in a good honest shift but obviously the sendings off affected us. Until he went Harpur was dominating the midfield.
“He was a big loss. We played well in the first half and scored an excellent goal.
“In the second half Halliday came on and turned the game in Glentoran’s favour and they went on to win quite convincingly with Glenavon down to nine men.”
McDonald said: “Ours was a good performance and that was pleasing. This was a big test.
“You have to match the passion of any team Marty Quinn puts on the pitch and we did that.
“When we went down to 10 men we gave 10 per cent extra.
“I’m glad this game went ahead because we cannot afford any more postponements. It’s becoming increasingly difficult to fit in fixtures.
“The Mourneview pitch was firm but playable and it’s good we were able to put more points on the board.”