Cardiff City manager Neil Warnock praised his players' resolve as they kept a clean sheet and beat Bristol City 1-0.
A goal from Kenneth Zohore in the last 10 minutes of the game was enough for the three points that keeps the Welsh side handily placed for a return to the Premier League.
I thought we had the better opportunities but it was always going to be close.Neil Warnock
Aston Villa's win on Saturday pushed them to within a point of the Bluebirds but Warnock's team have now restored a four-point gap and they moved to within six of leaders Wolves.
In a biting wind at the Cardiff City Stadium the teams looked like cancelling each other out before Zohore came off the bench and struck in the 82nd minute, converting a cross from Joe Ralls.
Afterwards Warnock said his side just about deserved all three points. He said: "It was never going to pretty. The pitch was terrible, the wind was bad, it was the coldest day of the year, the ball was lively and it was a derby.
"We said at half-time it would be a sloppy goal, make sure we don't make a mistake because it's a mistake which will cost the game.
"We're delighted to come out of it with three points. I thought we shaded it. I thought we had the better opportunities but it was always going to be close.
"And it was great to come out with another clean sheet - that was our target we set at the start of the season, 16 clean sheets. It's a great achievement."
The defeat means that Bristol City's hold on a place in the top six in the Championship is becoming more tenuous.
They remain in the play-off places in sixth place but they are now just two points ahead of Middlesbrough and Sheffield United.
Cardiff are 1/7 to be promoted with Steve Bruce's Villa priced at 11/10.
Bristol City are 1212/1 to finish in the top six of the Championship with Middlesbrough 1/10000.
View all Soccer betting