Defender Eric Lichaj taps in his second goal in 36 appearances this season
Huddersfield's automatic promotion hopes were dealt a further blow as Nottingham Forest gave manager Mark Warburton a fully-deserved first win.
Forest created a host of first-half chances and led when Ben Brereton squared for Eric Lichaj to tap in.
Town responded with Elias Kachunga steering a chance wide and Nahki Wells forcing Jordan Smith into two saves.
But Jamie Ward then pounced on Dean Whitehead's poor header to race through and beat Terriers keeper Danny Ward.
Forest had defeated both of Huddersfield's promotion rivals - Newcastle and Brighton - at the City Ground this season and, spearheaded by Brereton, could have won by more.
The 17-year-old hit the side-netting from an early counter-attack, and crossed for Jamie Ward whose point-blank header was kept out by Danny Ward's excellent save.
Town midfielder Jonathan Hogg also cleared Joe Worrall's header off the line and Zach Clough shot wide when well placed, while Forest's Ward forced his namesake into another good stop.
The Terriers had lost just twice in their 10 previous away league matches but after the opener it was Forest who provided the greater threat on the break, with Lichaj denied an unlikely double by Danny Ward's legs.
Huddersfield's third defeat in their last four matches left them 10 points behind second-placed Newcastle, who lost 2-1 at Sheffield Wednesday in Saturday's late kick-off, and 12 points adrift of Brighton with six games of the season to go.
Forest's first win in six league games, and only their second in 11, lifted them up a place to 19th, five points clear of the bottom three.
Nottingham Forest boss Mark Warburton:
"It is all about Friday now. We will do everything to make sure we are prepared for Blackburn and the details are key. Now we focus on that.
"The players will see the quality there today and they will see that they get their rewards; they have to believe that if they do things right and work hard, they will get their rewards. We saw that today.
"We are delighted with three points, which are vital at this stage of the season. But I was also delighted with the quality of the performance. I thought we moved the ball well, we were brave, we created chances and in truth we should have been two or three up by half-time.
"We expected a reaction from them and there was one. We had to weather the storm. But we kept the ball and created chance after chance. It was a very pleasing performance against a quality unit."
Huddersfield boss David Wagner:
"Today we did not perform and this was the biggest problem. We have to make sure we perform better. But we are human.
"We were second best, particularly in the first half. They surprised us with their set up. We were not expecting that.
"We were not able to make the right decisions, Forest had a three-man back line and were overloading the midfield. We were not able to catch them and close the gaps.
"We changed our formation at half-time and we were better. We had opportunities. But then we made a mistake - an unusual mistake - for the second goal.
"We left ourselves with a mountain to climb and we were not able to do it. We have six - and hopefully more - very important games still to play. We must move on quickly now."
