A goal from substitute Danny McKee two minutes into added time saw Glentoran beat Cliftonville at the Oval.
McKee got on the end of a long throw from Elliott Morris and lobbed the ball over Reds goalkeeper Conor Devlin.
David McDaid took a touch before firing the visitors into an 11th-minute lead but David Scullion replied with a left-foot strike from the edge of the box which was deflected over Devlin on 24.
Cliftonville now lie four points behind league leaders Linfield.
Joe Gormley cut in from the left and provided the pass for McDaid to score the opener and the prolific Reds forward then himself fired a shot in from outside the box but Morris managed to get a touch to push the ball wide.
After Scullion's equaliser, Devlin did well to save a Curtis Allen left-foot shot with his legs, while McDaid 's goalbound free-kick was saved low to his left by Morris.
McDaid squandered several opportunities for Tommy Breslin's side in the second half and, at the other end, Marcus Kane's header was brilliantly saved by Devlin.
Glentoran manager Eddie Patterson: "Cliftonville put us under pressure at times but we prepared for this all week - we produced a positive workrate and got in their faces.
"There's no better way to win a game than by scoring a goal in the last minute. It was only Danny's second or third touch, but he finished it well.
"That's three league wins in a row and it sets us up nicely for the big Boxing Day match with the Blues at Windsor Park.
"Our aim is to finish in the top six - we need a couple of experienced heads to help the young lads on, but they're gaining more experience all the time and we'll try and add a few new faces at the end of the season."