Having equalised and then been dominant in the second half, Rabs were hit by a sucker punch with four minutes remaining to leave Ayrshire with nothing to show for their endeavours.
Rob Roy were first to take the play to their opponents with Deas then Martin having shots blocked before Deas sent a corner flashing across the Glenafton goalmouth with no takers.
Glens began to force their way back into the game and took the lead in the 15th minute when Marlow was given space in the six yard box to rise unchallenged to send a McKernon corner kick into the net.
The hosts pushed forward for a second with Marlow’s well directed drive from the edge of the penalty box was well saved by Rabs keeper Wilson.
Rabs should have drawn level in the 23rd minute when Deas sent over a free-kick from near the right corner flag it was met by Brogan but his header from close range flew over the bar.
Play swung from end to end making it an entertaining match for the spectators, Wilson did well to save a McGill header then a Connolly volley before McKernon flashed a header past the post.
At the other end Deas had a goalbound shot blocked after a clever Sawyers lay off then on the half-time whistle home keeper McGarrity was forced to punch a 20 yard Deas free-kick to safety.
Rabs stepped up a gear at the start of the second half and took control of the match with substitute Duff prominent in Rabs attacks.
Sawyers headed a Deas corner over the bar then Morton brought out a good save from McGarrity.
In the 51st minute the Glens defence survived a goalmouth scramble which ended with a McGarrity save from a Ronald attempt.
The visitors domination paid off in the 62nd minute when Sawyers rose to crash a header from a Deas corner kick past McGarrity to put his side back on level terms.
Five minutes later Morton hit the Glens upright with Ronald hammering the rebound against the crossbar. Rabs continued to press forward with McGarrity pushing a Ronald drive over the bar then saving a Morton header.
Just as it looked like there was to be a share of the spoils Rabs were hit with a hammer-blow in the 86th minute when Kinney sent a pass across the Rabs penalty box, Connolly played the ball forward for ex Rabs player Findlay Frye to slam it into the empty net.