Match ends, Cardiff City 0, Nottingham Forest 1.
Nottingham Forest ended a run of six games without a win to put a huge dent in Cardiff City's play-off aspirations.
James Garner's 29th-minute strike in a crowded penalty area proved decisive as Forest produced an excellent defensive display in south Wales.
Kieffer Moore's second-half effort from close-range was as close as the hosts came to finding an equaliser.
The victory sees Forest rise to 16th in the Championship, while Cardiff are eighth, four points off the play-offs.
This success means Forest have earned consecutive away league victories against Cardiff for the first time, having also won 1-0 last season.
It is all the more surprising considering that the Bluebirds would have enjoyed the international break, buoyed by their win over Swansea City, but they were without skipper Sean Morrison, who sustained an Achilles injury at the Liberty Stadium.
The derby victory reignited Cardiff's hopes of a play-off spot, with Forest seemingly the ideal opponents according to the form book.
Cardiff had won 10 of their last 12 league meetings with Forest, with Chris Hughton's side winless in six heading into the international break and once again looking nervously over their shoulder at the relegation places.
Hughton made three changes with Joe Worrall making a welcome return from a cracked rib, with the defender soon in action as Cardiff produced a fine move after eight minutes, but Brice Samba was able to save Leandro Bacuna's shot.
Cardiff again came close on 20 minutes but Tom Sang headed over from Joe Ralls' fine cross.
The missed chances buoyed the visitors and after Sammy Ameobi's shot was blocked, they found the breakthrough when Cyrus Christie's pinpoint cross found Garner, with the Manchester United youngster lashing home unmarked.
Cardiff created little in the first half, with Curtis Nelson heading over and Harry Wilson shooting wide, but they did come close to an equaliser on the stroke of half-time when Will Vaulks hammered a half-volley from 25 yards that fizzed just wide of the upright.
The Bluebirds' intensity did improve after the break, but Moore's shot from just six yards out was incredibly blocked by a Forest defender, while Bacuna and Aden Flint both missed the target with half-chances.
Cardiff made a trio of attacking changes with 20 minutes remaining and changed their formation, but Samba saved from Marlon Pack on an afternoon where Cardiff looked short on inspiration.
However, they would have expected to level on 84 minutes when Josh Murphy's cross found Flint unmarked four yards out, but he headed over the bar.
Ciaron Brown also saw a late header saved as Cardiff bombarded Forest with set-pieces, but the visitors held firm.
Cardiff City manager Mick McCarthy told BBC Sport Wales:
"It was the classic game of two halves, they were better than us in the first half and managed to get the goal and probably deserved it.
"We didn't get going, but we had a great reaction in the second half and we were the best side but couldn't manage to get the goal.
"I know Chris' teams are hard to break down, they are a tough nut to crack, and we knew if they scored the first goal it would be tough, as it would for them if we got the first goal.
"The second-half reaction was good, we weren't at our best in the first half, but give Forest credit for that - we couldn't get going. We weren't at the standard we've been at."
Nottingham Forest manager Chris Hughton said:
"It was certainly a good win from a tough game. We expected nothing less coming here, they have a way of playing and they're in really good form at the moment so you know you will have to be strong and resolute.
"There were minimal chances and for us, we had that one piece of quality for the goal. We restricted them to one good chance that Flint had at the end.
"It was a tough game and performance, and when you win these games, sometimes it's an even better feeling.
"We had to battle, every player had to be resolute and we had to concentrate."
- 30BrownBooked at 37mins
- 21PackBooked at 14mins
- 6VaulksSubstituted forColwillat 84'minutes
- 8RallsSubstituted forWilliamsat 71'minutes
- 23WilsonSubstituted forMurphyat 71'minutes
- 7BacunaSubstituted forOjoat 71'minutes
- 10MooreSubstituted forM Harrisat 84'minutes
- 29M Harris
- 2ChristieBooked at 26mins
- 18Ribeiro DiasBooked at 87minsSubstituted forColbackat 87'minutes
- 7GrabbanBooked at 55minsSubstituted forTaylorat 72'minutes
- 6Mbe Soh
- Gavin Ward
- Shots on Target
Second Half ends, Cardiff City 0, Nottingham Forest 1.
Attempt missed. Marlon Pack (Cardiff City) right footed shot from outside the box is high and wide to the right. Assisted by Josh Murphy following a set piece situation.
Jonathan Williams (Cardiff City) wins a free kick in the attacking half.
Foul by Jack Colback (Nottingham Forest).
Foul by Curtis Nelson (Cardiff City).
Lyle Taylor (Nottingham Forest) wins a free kick in the defensive half.
Substitution, Nottingham Forest. Jack Colback replaces Cafú.
Cafú (Nottingham Forest) is shown the yellow card.
Aden Flint (Cardiff City) wins a free kick in the defensive half.
Foul by Cafú (Nottingham Forest).
Attempt missed. Ciaron Brown (Cardiff City) header from the right side of the six yard box misses to the left. Assisted by Josh Murphy with a cross following a corner.
Corner, Cardiff City. Conceded by Ryan Yates.
Marlon Pack (Cardiff City) wins a free kick in the defensive half.
Foul by Sammy Ameobi (Nottingham Forest).
Attempt missed. Aden Flint (Cardiff City) header from the centre of the box is just a bit too high. Assisted by Josh Murphy with a cross.
Substitution, Cardiff City. Rubin Colwill replaces Will Vaulks.
Substitution, Cardiff City. Mark Harris replaces Kieffer Moore.
Offside, Nottingham Forest. Lyle Taylor tries a through ball, but Cafú is caught offside.
Offside, Nottingham Forest. Cyrus Christie tries a through ball, but Sammy Ameobi is caught offside.
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