The Reds' star on the day was Lansbury, who converted a 44th-minute penalty to double the lead after Robert Tesche opened the scoring, before bagging his brace on 70 minutes after Matt Smith had given the hosts a lifeline.
Despite the three points, Cohen has claimed results like this make him more frustrated because it proves to him what he and his team-mates were capable of all along, though he singled out the ex-Arsenal man for special praise.
“It’s been a very frustrating and disappointing season in so many ways and results and performances like this probably make it more frustrating because it shows how good we can be," he told their official website.
“I thought we dominated the game. They had a 15-minute spell when Matt Smith came on – they pumped balls into our box and he caused a bit of a problem.
“Once we started keeping the ball we looked threatening again and having Henri Lansbury, who for me is our best player, playing in his best position is the way to win football matches.”
It has been a tricky all-round season for Forest, whose campaign took another hit last month when the club sacked manager Dougie Freedman, who was replaced on an interim basis by Paul Williams.