Glenavon scored two late goals to come from behind and snatch a 2-1 win over Glentoran at the Oval.
Darren Murray's first-half penalty had given the Glens the lead as they chase a Europa League play-off place.
But Glenavon manager Gary Hamilton came off the bench to force an equaliser before Conor McCloskey sprung the offside trap to grab a dramatic winner.
The Lurgan side's second consecutive league win leaves them six points adrift of third-placed Crusaders.
The Mourneview men still have a game in hand over the defending champions as they attempt to revive their form following a disappointing run of results since the start of 2019.
Glentoran's second defeat in their last six league outings leaves the east Belfast club ninth in the table and two points behind seventh-placed Dungannon Swifts, who have played one game more than Gary Smyth's side.
Murray punishes early Mourneview misses
Glentoran had the first chance of the night when John Herron robbed Seamus Sharkey of possession but the midfielder's cut-back got trapped under the feet of Robbie McDaid as he lined-up a shot.
But it was the visitors that dominated the opening half hour with the pace and movement of Cameron Stewart and Andrew Mitchell creating problems for the Glens' defenders.
Stewart was unable to find the target with a couple of close-range headers before Mitchell's left-footed curling shot forced a sprawling one-handed save by Glentoran goalkeeper Dwayne Nelson.
Playing on the counter-attack for most of the opening 30 minutes, Glentoran's best chance came from a miss-hit cross by McDaid that forced Jonny Tuffey to claw the ball out from under his crossbar.
The hosts took the lead in the 39th minute following a reckless challenge by Glenavon's Caolan Marron on McDaid as the striker chased after a rebound that was heading away from goal and Murray produced a composed finish from the penalty spot.
The visitors had a chance to equalise just before the break but Sharkey was off balance as his volley glanced off the crossbar and over while Stephen Murray could not keep his header on target from the first attack after the restart.
Hamilton makes the difference
A turgid second half produced little goal-mouth action as Glentoran comfortably defended their lead until Hamilton's decision to introduce himself for the injured Andrew Mitchell in the 75th minute.
The 38-year-old quickly made his presence felt against his former club as he plundered the equaliser in the 81st minute.
The Glens' defence allowed a long throw to bounce in the area and Hamilton showed his experience to get a toe on the ball and steer it past Nelson at his near post.
Glentoran were still reeling from the goal just seven minutes later when McCloskey broke from midfield and raced onto an aimless ball through the middle before lifting his shot over the on-rushing keeper for a stunning winner.
The home side introduced Curtis Allen in a desperate attempt to salvage a point but they could not find another goal in a repeat of the last encounter between the two sides when the Glens also allowed a one-goal lead to slip in October.