Montrose stiker Craig Smart put a massive dent in Gretna's promotion hopes as he hit a second half double.
The Gable Endies pulled off a smash and grab raid as they came back from a goal behind to send the Borderers crashing to their third home defeat of the season.
Goal hero Smart said : " We battled away well and took our chances. " Gretna hit man Martin Cameron fired the home side in front in the sixth minute, Derek Townsley played a clever ball over the top and Cameron showed great composure to volley over advancing keeper James Butter and into the roof of the net for his 17th goal of the season.
His strike partner Ian Stevens could have put Gretna two up six minutes later but shot wide after Butter had parried a Cameron header.
Montrose saw Kevin Webster, Steven Kerrigan and Smart all come close before the break but they were unable to bring the Gable Endies level at the interval.
Smart finally levelled the scoreline in the 51st minute when Gretna suffered a mix up at the back and Webster crossed for him to guide a shot into the corner of the net from close range.
Smart was on the mark again in the 74th minute when Lee Maddison left a back pass short and Martin Wood nipped in to fire against David Mathieson leaving Smart on hand to slot home the rebound.
Gutted Gretna boss Rowen Alexander fumed : " I'm bitter and absolutely disgusted with the attitude shown today. I was expecting more from a team who are full-time but they turned in a dismal show in front of a bumper crowd.
" It's been a big damage to our promotion hopes and we now have 12 finals to the end of the season. " Montrose boss Henry Hall said : " it was a good performance and we played with a lot of spirit and battled hard for the points".