IT took morning leaders Ballymena United just 72 seconds to open the scoring courtesy of Gary McCutcheon who turned home an Allan Jenkins header from an Aaron Stewart free-kick.
And they doubled their advantage on five minutes through a Jordan Baker close range finish after McCutcheon set Alan Teggart free to deliver a left wing cross.
McCutcheon further extended their lead on 32 minutes from the spot after Jonny Magee had brought down Jenkins inside the area.
But the Glenavon fightback began five minutes later through Mark Haughey with a back post header in off the bar from a Niall Henderson corner.
Then, two minutes later, they reduced the deficit to a single goal when former United striker Kevin Kelbie swivelled on the spot to turn a Peter McCann header past 'keeper Aaron Kerr.
Ballymena's gradually declining afternoon got worse four minutes into the second half after Aaron Black picked up his second booking for dissent.
Glenavon almost made their numerical advantage count on 70 minutes when Jonny Magee rattled the bar from a Henderson corner.
But that third goal to complete the comeback did arrive three minutes from the end when Henderson slotted past Kerr after meeting a Kelbie through ball following some poor home defending.
Ballymena United: Kerr, Rodgers, R. Black, Munster, Stewart, Baker, Surgenor, Jenkins, Teggart, Costello, McCutcheon subs A. Black (replaced Surgenor 42), Woods (not used), Boyd (not used), Murray (not used), Carson (replaced Teggart 79)
Glenavon: Coleman, Shannon, Neill, Jay Magee, Haughey, Henderson, O’Carroll, Kelbie, D. Magee, Jonny Magee, McCann subs Miskimmin (replaced O'Carroll 59), Doherty (replaced McCann 83), Turkington (not used), Graham (replaced Jonny Magee 73), O'Hare (not used)
- Niall Henderson celebrates after grabbing Glenavon's late equaliser (Picture: Gareth Irvine/PressEye.com)