Sunderland closed in on the Sky Bet Championship play-off places by beating Middlesbrough 2-0 to secure their first Tees-Wear derby win in over a decade.
The Black Cats had not beaten their local rivals since an FA Cup tie in February 2012, but ended the run with a dominant performance that moved them up to ninth in the table on 41 points, a point outside the top six.
Ross Stewart - who had a first-half strike ruled out for offside - gave Tony Mowbray's men the lead by tapping in after Zack Steffen had saved his penalty (51), with Dael Fry sent off as the last man after conceding the spot-kick.
Manchester United loanee Amad Diallo made sure of the victory with a stylish finish late on after intuitive link-up play with Patrick Roberts (81).
Middlesbrough stay sixth as a result of their four-match winning streak concluding at the Stadium of Light.
How Sunderland reiterated their play-off credentials
Though, arguably, the lesser of the north east's derby matches, with Sunderland and Middlesbrough both having their eyes on promotion back to the Premier League, the encounter was hotly contested from the start.
With just under 10 minutes gone, Sunderland were presented with a gift when Steffen's hasty clearance flew straight to Diallo, who composed himself with a neat touch, but then fired across the face of goal.
The hosts suffered a blow shortly afterwards when captain Corry Evans was forced off following a clash of knees with Riley McGree, having initially tried to run off the knock.
They continued to look the more threatening of the two sides, though, and thought they had taken a deserved lead when Stewart fired into the roof of the net after Steffen had spilled Roberts' shot, before the offside flag curtailed any celebrations.
Sunderland's organisation at the back meant Boro toiled in the final third, with their closest chance of the first half coming when Anthony Patterson tipped a low shot from Marcus Forss around the post.
The game sparked into life quickly after the restart, when Stewart chased down a long ball and, with his foot on the 18-yard line, was pulled back by last man Fry, who conceded a penalty and was then shown a straight red card by referee James Linington.
Steffen guessed correctly and kept out Stewart's initial spot-kick, only for the Scottish striker to tap home the rebound to take his tally for the season to 12 goals in 15 games.
Boro came close to an equaliser when McGree collected Chuba Akpom's pull-back and rolled a shot inches wide of the right-hand post, but the game was put beyond their grasp with nine minutes of the 90 to play, when Diallo exchanged passes with Roberts and curled in an emphatic second.
Player of the match - Amad Diallo
The managers
Sunderland's Tony Mowbray:
"I had a long conversation with the people at Manchester United about Amad this week and how well he's doing. The test for him is when he goes back next year; can he have a good pre-season? Does he feel like a first-team player there? That's the glass ceiling he has to break through, really.
"Harvey Elliott was at Blackburn Rovers a couple of years ago; he broke through that ceiling at Liverpool and plays, a lot of the time, in the first team now. Amad has to try and do that and he's not going to fall short on talent.
"For me, with these young players, it's all about their personality and whether they feel they can do it and feel they should be on the pitch with Bruno Fernandes and all the big players at Manchester United. I hope so, because he's very talented, he's a lovely kid, he's very humble and you hope he can produce it at the top level."
Middlesbrough's Michael Carrick:
"It [the penalty] was outside the box, first and foremost. Dael didn't deliberately try to bring him down; I think they were just running next to each other and Ross has ended up falling down. He's within his rights to do that - I'm not blaming him for going down. But there wasn't a grab, there wasn't a pull, a push or a trip or anything.
"It wasn't deliberate, by any stretch, and it wasn't in the box, so I can't understand how they can give a penalty for that and send him off.
"It was difficult. I thought the boys did really well with 10 men for a good spell and I thought we actually reacted well, dealt with it well, looked solid enough defensively and definitely looked a threat on the break. If anything, I thought, the longer the game was going, I fancied us to get back into the game. I thought we'd end up scoring towards the end and unfortunately it didn't quite work out."
What's next?
Both teams are back in action at 3pm on Saturday January 28 in the fourth round of the FA Cup.
Sunderland travel to Craven Cottage to take on Fulham of the Premier League, while Middlesbrough host Championship promotion rivals Watford at the Riverside Stadium.