Niall McGinn's deflected strike three minutes into injury-time saw Glentoran beat Portadown 2-1 at Shamrock Park.
Declan Devine's side had looked on course for victory thanks to Jordan Jenkins early goal, but Ryan Mayse equalised with 13 minutes remaining.
Just as the game looked set to end all square, McGinn's effort from outside the box struck a Portadown defender and looped over former Glens keeper Aaron McCarey.