Eddie Howe said he was to blame after Newcastle lost the first Tyne-Wear derby in over 10 years at St James' Park.
Brian Brobbey's 90th-minute winner completed what had looked an unlikely comeback for Sunderland when an in-command Magpies took an early lead through Anthony Gordon.
However, the defeat sees the Black Cats climb above their rivals in the Premier League and break a new record for 11 consecutive Premier League Tyne-Wear derbies without defeat.
Club legend Alan Shearer took to social media after the game to describe the second-half display as "pathetic, weak, lazy and limp," and Howe has accepted responsibility for the result.
"Very painful. Most of all, painful for supporters. They're the ones I think about now," Howe said in his post-match press conference.
"Once you haven't performed and you know the size of the game and you don't deliver, you expect to be criticised and you understand why. I understand the reaction at the end. We haven't done our jobs well enough today and we're desperately disappointed in ourselves.
"I'm fully committed to the job. I'm disappointed in my delivery today and my delivery in the last week. The Barcelona game was very tough, today was even tougher. As I said after the Brentford game, I absorb that blame myself.
"I don't look to deflect it anywhere and I certainly won't deflect it to my players. I protect my players until my last breath. That's how I look at it and it's going to be a tough, painful few days for me."
Howe's afternoon was not helped when it was revealed that midfielder Sandro Tonali would not be fit to make the matchday squad having picked up a groin injury in the game against Barcelona in midweek.
The Italian joined Bruno Guimaraes and Lewis Miley on the sidelines, and Howe believes their absence negatively impacted the balance of the engine room he selected to play.
"We missed our midfielders that would give us that control and that technical delivery - Bruno, Lewis Miley and Sandro," he added.
"Missing all three of those players left us slightly unbalanced. That was the main consequence of that poor technical delivery, we lost the control of the game we had in that first half.
"Then the game became transitional. We're slightly fatigued, then we look even more tired and then we make more mistakes. My first thought is to point at the technical delivery. We made the game too much like they wanted it and that didn't help us."
The defeat leaves Newcastle 12th in the Premier League table, seven points behind fifth-placed Liverpool. Despite that, Howe does not believe they are far away from their top level.
"It's very easy to look at all bad, but I don't think we're too far away. Our recent form has been inconsistent. It's been patchy - it's been patchy all season.
"We've had good bits, we've had bad bits. I felt, all along, that we've steadily got a bit better than we were early season. Probably the progress hasn't been as quick as I'd have wanted it to be. But some of the fixtures we've had, particularly in recent weeks, have been unrelenting for us."
The Tyne-Wear derby was the Magpies' 51st game already this season, and while Howe is quick to avoid using fatigue as an excuse, he acknowledged that his side have not been able to keep up with their desires for more free-flowing football.
"It's an incredible amount of points and there's huge regret from us on that," he added.
"Certainly from my side, there's no part of me that ever wants to take the lead, then sit on a lead. The opposite. We want to go for more goals, that's always been in our psychology in coaching, to continue to attack, continue to be front foot, but we haven't been able to maintain that for whatever reason.
"We've become very passive, quite reactive and we were again today and that's a huge disappointment."
Analysis by Your Site' Callum Bishop:
Eddie Howe might not be willing to use fatigue as an excuse for Newcastle's performances, but it is clear that it is an inescapable issue at St James' Park.
Fifty-one games by March is an extreme number. In a sense, the Magpies are the architects of their own downfall by being too successful. Progressing in cup competitions has not helped them with their workload and being eliminated from Europe by Barcelona could be a blessing in disguise for the remainder of the season.
What was obvious against Sunderland is that Howe's men lost control. Going into the break, it was all relatively comfortable. But, 1-0 is a dangerous scoreline, especially when your energy levels are rapidly depleting.
It's almost as if Newcastle need to build a big lead in the first 45 minutes of games where they are fresh in order to avoid a capitulation in the second when they have nothing left in the tank. At the top level, that is easier said than done. Ultimately, Howe has to make it work with who he has from now until May.
