Full-time: Newcastle United 0 Sunderland 3
Goals from Fabio Borini, Adam Johnson and Jack Colback ensured the Black Cats made it three derby wins succession for the first time since 1924.
The visitors completely outplayed their shell-shocked opponents as they put further distance between themselves and the bottom three.
Newcastle were left reeling, and the anger at the events of the final week of the transfer window boiled over late on as two supporters invaded the pitch.
It was a remarkable afternoon, with Sunderland completing a rare double over the Magpies following their 2-1 win on Wearside earlier this season.
Both sides named their January attacking acquisitions on the bench, with Luuk de Jong lining up among the Newcastle substitutes and Ignacio Scocco featuring among the Sunderland replacements after his international clearance came through late on Friday evening.
There was a Black Cats debut for Liam Bridcutt though, with the midfielder replacing Seb Larsson little more than 24 hours after completing a £3m switch from Brighton.
Newcastle boss Alan Pardew made one change to the side that had drawn at Norwich four days earlier, with Shola Ameobi replacing the injured Loic Remy in attack.
The hosts had been the better side at Carrow Road despite failing to make a breakthrough, and they began brightly again with Mathieu Debuchy dragging a second-minute shot wide after bright approach play from Moussa Sissoko.
The early stages were typically frenetic, with both sides flying into tackles and pouring forward at every opportunity, and Sunderland should really have claimed the lead with their first chance of the game.
Johnson delivered a free-kick from the right, but Marcos Alonso headed wastefully over the crossbar after finding himself unmarked on the edge of the six-yard box.
John O'Shea picked up the first booking of the game for a foul on Sammy Ameobi in the 13th minute, and from the resultant free-kick, Davide Santon curled a tame shot into the arms of Vito Mannone.
Santon was a prominent figure in the opening 15 minutes, and after playing a slick one-two with Hatem Ben Arfa, the full-back shot over from the edge of the box.
Suddenly, however, Sunderland broke into life, and two goals in the space of four minutes completely transformed the mood inside St James' Park.
Borini scored the first from the penalty spot, profiting from Vurnon Anita's rash challenge on Phil Bardsley.
Johnson slipped a wonderful ball inside to the full-back, taking two Newcastle defenders out of the game, and Anita panicked as he chopped Bardsley down close to the edge of the area.
Borini stepped up and rifled his spot-kick into the roof of the net, but was booked for his celebration in front of the Leazes End.
The Sunderland fans in the away end were in raptures at that point, but their joy was even more pronounced minutes later as the visitors doubled their lead.
This time it was Jozy Altidore unlocking the Newcastle defence with a wonderful pass as he played in Colback.
Krul saved the midfielder's shot after it deflected off Steven Taylor, but Johnson was on hand to tap home the rebound and claim his sixth goal in the last four league games.
Newcastle were completely rattled, and while Anita shot over after breaking into the box, the hosts looked troubled whenever Sunderland's attacking players ran at them.
With the much-maligned Altidore holding up the ball and linking play superbly, Sunderland continued to pour forward as half-time approached and Johnson headed Alonso's left-wing cross over the bar.
Alan Pardew would have been desperate to get his side into the dressing room, and the Magpies manager made a half-time alteration as he introduced debutant de Jong for Sammy Ameobi.
The Dutchman fired in the first effort of his Newcastle career five minutes after the break, but it was a tame effort that trickled through to Mannone.
Sunderland remained on the front foot for the majority of the second half though, and Johnson threatened to claim his second goal of the game when he curled a free-kick over the crossbar shortly before the hour mark.
Mannone hadn't really been tested at that stage, but the Sunderland goalkeeper was finally forced into a top-class save in the 64th minute. He proved up to the task, flinging himself to his left to claw away Cheik Tiote's goalbound shot.
Newcastle went close from the resultant corner, with Shola Ameobi directing a diving header wide, but with the game flowing from end to end, Sunderland came within inches of grabbing a third goal.
Johnson, who is in the best form of his Black Cats career, beat both Paul Dummett and Sissoko in the area before curling an excellent strike against the base of the left-hand post.
Newcastle desperately needed a way back into the game, and it almost arrived in the 73rd minute. Amoebi rose highest to reach a corner from the left-hand side, but Borini nodded the ball to safety from his position on the post.
Gaps appeared at either end late on, and Altidore wasted a glorious opportunity when he failed to round Krul despite being left with a clear run on goal.
Sunderland didn't have to wait long for a third goal though, with Colback inflicting yet more misery on Newcastle with ten minutes left.
Colback won possession from Ben Arfa, fed Borini, and received the ball back from the Italian before drilling an excellent finish into the corner.
That was the cue for two separate pitch invasions, with the fury from the home fans inside St James' Park reaching boiling point. At least one of the pitch invaders appeared to be trying to throw away his season ticket in front of Pardew.
Newcastle (4-2-3-1): Krul; Debuchy, Williamson, S Taylor, Santon (Dummett 64); Tiote, Anita (Marveaux 75); Sissoko, Ben Arfa, Sammy Ameobi (de Jong 46); Shola Ameobi.
Subs (not used): Elliot (gk), Haidara, Yanga-Mbiwa, Armstrong.
Sunderland (4-1-4-1): Mannone; Bardsley, Brown, O'Shea, Alonso; Bridcutt; Johnson (Larsson 77), Colback, Ki, Borini (Gardner 89); Altidore.
Subs (not used): Ustari (gk), Vergini, Giaccherini, Wickham, Scocco.