Sunderland hung on to beat Championship strugglers Derby County to move up to third in the table, despite bizarrely having a Wilson Isidor goal disallowed in the second half.

There was no suggestion of the offside flag being raised before the forward crashed home what would have been the Black Cats' second goal of the night, with the celebrations going on for about 30 seconds before referee Sam Allison said it would not stand.

Earlier, Eliezer Mayenda ran onto a deflected from Jobe Bellingham to coolly slot his shot under Rams goalkeeper Jacob Widell Zetterstrom for the opening goal in a tense first half at Pride Park.

Isidor went on to have a potential goal-of-the-season contender blocked after running the length of the field, before controversially having his second ruled out in an absorbing second half.

Derby were lively as they pressed for an equaliser, with Norwegian striker Lars-Jorgen Salvesen particularly threating on his debut, but they failed to do enough to avoid a sixth straight defeat in all competitions.

There had been boos for Rams boss Paul Warne and his players at Pride Park following Saturday's defeat by Watford, but a spirited performance and mounting injury problems – which was only made worse by the loss of both Kane Wilson and Dajaune Brown to apparent hamstring problems – ensured the jeers were largely muted this time.

In-demand defender Eiran Cashin, who is said to "categorically" not up for sale in January, was left out of the squad as a precaution after only returning from a hamstring injury at the weekend.

And with fellow centre-back Curtis Nelson having his season ended by an injury in that same game, it meant Warne was forced to shift midfielder Ebou Adams into a makeshift back three.

Isidor, who remarkably had two late penalties saved by James Trafford in Sunderland's goalless draw with Burnley four days earlier, was first to test Derby's Swedish keeper Zetterstrom with a swerving effort midway through a first half of limited opportunities.

The finish that Mayenda slid between Zetterstrom's legs was only their second shot on target.

Bellingham burst forward to tee the Spaniard up after Chris Rigg recovered the ball on the halfway line when he initially gave up possession with a sloppy .

Enzo Le Fee went on to force Zetterstrom into a diving save with an excellently struck free-kick from 25 yards before the break, while a desperate sliding block from Kenzo Goudmijn denied Isidor what would have been a memorable goal.

The striker came up with the ball on the edge of his own penalty area as they defended a corner, then set off on a stunning solo run which was only checked by backtracking Dutchman Goudmijn as Isidor tried to pick out the bottom corner.

Derby threatened either side of that chance, with Nathaniel Mendez-Laing having a fierce shot blocked before substitute Salvesen had two headed attempts kept out by Sunderland goalkeeper Anthony Patterson.

Sunderland thought they had gone 2-0 up in the 77th minute, with Le Fee controlling a searching ball from Bellingham before linking up with Isidor, who crashed his shot home off the underside of the crossbar.

There was disbelief as the goal was later disallowed, leaving players and Sunderland coaching staff searching for answers from the match officials at full-time.

Derby County head coach Paul Warne told BBC Radio Derby:

"I thought second half we played with more intent. No fan wants to hear this off of their manager, no doubt, but if you are going to lose then that is the way to lose.

"You've got to try and put your personality on the game, you have to put crosses in the box, make the keeper make saves and give the fans something to cheer.

"I didn't think we did that in the first half and I was expecting bigger boos at half-time, truth be told. I appreciate everyone that got behind the team and the team needed it.

"All in all I'm proud, but hugely disappointed that we didn't get anything."

Sunderland head coach Regis Le Bris told BBC Radio Newcastle:

"I don't know, really [about why Isidor's goal was disallowed].

"Maybe with VAR we could analyse the first ball and maybe an offside, but I don't think it was that decision. It was higher up the pitch and at the moment we don't know.

"It could have changed the outcome of the game, but at the end it was another tough game and the balance was different for the duration.

"We started maybe a little slowly because they are direct, and then after 15 minutes were good and created many chances in the first half. And if you don't score the second goal, you know that the opponent will believe until the end and it happened like that.

"It's good for our character because it shows that even in these circumstances we are ready to defend until the end.

"I'd also like to have a more relaxed end to the game because it's important to avoid last-minute equalisers, and we have had them before."