Glenn Murray's solitary strike was enough for Crystal Palace as they won their first league game in eight.
The 28-year-old struck soon after half-time, slotting home after a neat turn by Wilfried Zaha to condemn Nottingham Forest to their fourth straight defeat.
It was a fifth goal of the season for a player who recently hit a Carling Cup winner against Manchester United.
Steve Cotterill's Forest remain in the relegation zone having not scored in their last four games.
The goalscorer could have put Palace ahead early on but Forest goalkeeper Lee Camp saved well from his 25-yard drive.
Former Liverpool winger Paul Anderson's shot was blocked by defender Anthony Gardner as Forest pushed for the opener.
Lewis McGugan could have scored but headed narrowly over from Andy Reid's cross.
Murray was the hero for Palace, though, as he ended their long wait for a Championship victory.
Nottingham Forest manager Steve Cotterill: "We could have been 4-0 up at half-time and ended up winning the game six.
"There is not a lot wrong with us and we played some fantastic football. But it's not a big secret that we struggle to score goals.
"If we had a regular 20-goal-a-season man we would not have lost the games we have come to the stage when one or two of our strikers have got to come to the fore.
"We have tried all sorts of permutations, we work on our finishing in training but we have got to find a way of taking chances and getting on the end of all the crosses that go into the opposition box."
Crystal Palace manager Dougie Freedman: "It was a fantastic result and the performance merited it.
"Forest are a good team with good attacking players but we stood up to them and got our rewards.
"We showed a lot of spirit and pride to come away with a result. Our performances recently have been good but we have not been getting the crucial goals. Today we did.
"We are a growing team and a growing club and to be sitting in the top half of the division and in the semi-final of a cup is great. The good thing is that we are getting better all the time."