Alan Pardew has told his Newcastle players they must show fight in their final five games of the season in order to put their Tyne-Wear derby thrashing behind them.
The Magpies were beaten 3-0 by Sunderland, and Pardew described it as one of his worst days as the club's manager.
"It's about us making sure we put performances in from now until the end of the season that can help to ease the memory of this defeat - because it ain't going to go away," he said.
"We'll have to wear it [the defeat], probably next year as well. That's what happens when you lose one of these games.
"We're under no illusions as to the responsibility we have to our fans - and we've let them down, 100%. I don't think it's ever not going to affect the manner of my season, a defeat like that. To our fans, that's everything.
"We just have to make sure that in the last five games we put it right and get some work done on the training ground."
He said Newcastle "just didn't perform" in the manner he would have wanted but said they had been affected by Thursday's Europa League game against Benfica at St James'.
"After Thursday night, we couldn't really do much because of the [energy] levels of those players," Pardew, who made five changes from Thursday's starting line-up, explained. "Three or four of those players never trained after Thursday - they just had a short warm-up and a massage and went out again."
Meanwhile defender Mathieu Debuchy said he hoped Sunday's defeat would be the first and last time he suffers such disappointment in a Newcastle shirt.
Along with the Magpies' other January arrivals, Debuchy was sampling his first Tyne-Wear derby and was one of the few home players to come out of the game with any credit.
"It was an important derby both for the club and for the fans so we're really disappointed," he told nufcTV. "I can totally understand that they are upset.
"We didn't quite get up for this derby, but we're going to go out there and fight until the very end, starting next weekend.
"Even the new players knew exactly how important this was. We really wanted to go out there and win. We'll learn the lesson and do better next time. I hope it will be the first and last time [he experiences a game like that]."