Scorers: Slater (83) and McCluskey (86)
Two goals in the final 10 minutes dealt Stranraer’s play-off hopes a potentially fatal blow.
The Blues came into the game looking to bounce back from a 1-0 defeat at Stirling Albion and knew victory would close the gap on Edinburgh City, who drew on Friday night.
However, strikes from Craig Slater and Stefan McCluskey ensured it was Forfar, who will have their own play-off journey to look forward to, that picked up three points.
Jamie Hamill made one change from the side that lost seven days earlier.
Club captain Grant Gallagher returned in place of James Hilton, who was named on the bench.
It was a game of few clear cut chances with neither goalkeeper truly tested over much of the 90 minutes.
Stranraer’s best chance of the first half came from a Dean Hawkshaw free-kick.
The former Kilmarnock man floated a ball into the box and Tommy Muir managed to get a head to it but the effort drifted wide of the upright.
Darren Whyte sliced a shot wide at the other end and Marc McCallum smothered a loose ball, which seemed to hit off Muir before the half time interval.
Even at half time it looked as though the first goal in the game was going to be crucial.
As time went on – and neither team carved out clear-cut chances – it looked even clearer that would be the case.
Unfortunately, with seven minutes left to play, it fell the way of the visitors.
Stranraer failed to deal with a cross into the box and Slater blasted home from the edge of the box.
Before the hosts had a chance to react the game was wrapped up.
The Blues were napping at a throw in and Matthew Aitken flicked the ball on.
McCluskey outpaced Ayrton Sonkur before lifting his finish beyond the reach of Luke Scullion.
A desperately disappointing showing which surely all but ends Stranraer hopes of reaching the top four.
It is still mathematically possible but it will take something special over the remaining four games, starting with Albion Rovers away next weekend.
Stranraer: Scullion, Burns, McIntosh, Sonkur, Ross, Brady (Mullen 85), Gallagher, Hawkshaw, Watson (Walker 79), Muir, Woods (Yates 68).
Not used: Ellis, Robertson, Smith, Hilton and Baker.
Forfar Athletic: McCallum, Meechan, Strachan, Whyte, Munro, Slater, Warnock (Anderson 68), Harkins (Moore 89), Shepherd (Thomson 81), McCluskey (Thomas 89), Aitken.
Not used: Fisher and Sanderson.
Referee: Iain Snedden