Matthew Green netted three minutes into stoppage-time to give Torquay victory.
Rovers went ahead four minutes into first-half stoppage time when Jonathan Smith fired into the top corner.
After the break Elliot Benyon levelled when he smashed in from 20 yards and Torquay were then given a let-off when Adriano Rigoglioso missed a penalty.
And in stoppage time, Green fired home from 20 yards after being teed up by D'Sane to complete their comeback and take all three points.
Forest Green boss Jim Harvey told BBC Radio Gloucestershire:
"Considering we're in the middle of a bad run - which is obvious - with injuries and suspensions and we're struggling to get a team out, I thought the boys were absolutely first class."
"It was a tightly fought game, if the penalty goes in, then the game's over at 2-1 - it was a poor miss from Celi [Adriano Rigoglioso], and we got sucker punched in the last minute."
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