Leeds moved back to within four points of Sky Bet Championship leaders West Brom on Wednesday night, as Mateusz Klich scored the only goal in a narrow 1-0 victory at the Riverside Stadium.
In a scrappy first half, visiting striker Patrick Bamford spurned several chances to end his barren spell in front of goal, but before the break, Klich struck his fifth goal of the season and what proved to be the winner via the inside of the left-hand post (45+1).
With Leeds' promotion bid continuing to pick up pace, they remain second in the table, five points clear of Fulham - who edged past Swansea 1-0 at Craven Cottage. Middlesbrough, meanwhile, sit 21st, kept out of the bottom three by Wigan on goal difference alone.
How Leeds kept their title hopes on track
Each and every game in the Championship carries significance at this stage of the season, but with their own battles to fight at opposite ends of the table these two former Premier League clubs needed the points more than most on Teesside.
It was the hosts who took the game by the scruff of the neck, with Hayden Coulson creating problems with surging runs down the left channel, though Bamford - who had scored in just one of his previous 11 outings - passed up chances when he headed straight at Aynsley Pears and then guided a shot the wrong side of the left-hand post.
The Boro goalkeeper, 21, is proving to be a worthy replacement for his predecessor Darren Randolph and showed why with another smart save to deny a close-range Stuart Dallas effort, with Helder Costa blazing the loose ball high over the crossbar.
But he could do little to prevent his side falling behind in first-half stoppage-time. Spanish veteran Pablo Hernandez was initially denied by the right-hand post, but he collected a hashed clearance from Ryan Shotton and found Klich, who arrowed a low shot over the line via opposite upright.
Leeds boss Marcelo Bielsa made just one change from the side that beat Reading 1-0 at the weekend, with Gaetano Berardi replacing Kalvin Phillips.
Middlesbrough's Jonathan Woodgate, however, opted for three changes as he looked to avenge the 1-0 defeat to Barnsley. Hayden Coulson, Adam Clayton and Marcus Tavernier started in place of Marvin Johnson, Ravel Morrison and Britt Assombalonga.
With just one goal in it, Jonathan Woodgate's troops had a spring in their step as the second period wore on and though they too hit the woodwork, they were slightly less fortunate, with Marcus Tavernier's sumptuous first-time effort looping up over Kiko Casilla and bouncing clear.
They did have one more chance to restore parity late on. A Jonny Howson free-kick from 25 yards appeared to be blocked by the hand of Stuart Dallas, but as referee Gavin Ward waved play-on, Tavernier could only send a deflected drive into the waiting clutches of Casilla, who kept his third straight clean sheet.
What the managers said...
Middlesbrough's Jonathan Woodgate: "Miles better than the last two games, light and day between the performances. If we play like that we will be fine because everything was there - work ethic, determination. We were OK, at times on the ball we were poor but I thought we matched them really well. It's the same as when we went to Leeds, it's the last 20 seconds of the half. All you've got to do is turn and put it in the corner and he's 's played a square pass.
"The save gets blocked, they go down the other end and they score. That's the frustrating thing. By the way I thought we should have had a penalty from Lewis Wing's free-kick, I thought it was a clear handball, it didn't get given so you move on. They are going to be disappointed in there; I expect them to be disappointed no matter what if you lose games, but they are still there and they are still fighting and they'll keep on fighting. It's tight, it's even tighter now isn't it but I concentrate on our team, that's the best thing to do."
Leeds' Marcelo Bielsa: "The team fought a lot and were very aggressive. We attacked better in the first than second half. Today the team protected the result. We played well in different moments of the match. The team didn't lose their calm and fought. In general we managed the situations well.
"Maybe in some moments in the second half Middlesbrough created some problems but in general we had three more chances than them. There was a lot of fight in the match. We resolved well the absence of Kalvin Phillips. We were compact and tough to play. Scoring is the most difficult thing in football and more efficient teams do better."
Man of the match - Mateusz Klich
Perhaps the Polish midfielder was an easy choice due to the fact his goal settled the game in Leeds' favour, but was a real all-round force in midfield, making six tackles and providing three key passes on the way.
It's easy to forget he was sent out on loan to Utrecht after failing to settle in 2017/18, but Marcelo Bielsa has brought the best out in him over the past two years, rendering one of the first names on the team sheet.
Both sides are in action live on Sky Sports Football across the weekend. On Saturday at 12.30pm, Leeds travel to the KCOM to take on Hull, while on Monday at 7.45pm, Middlesbrough host automatic promotion-chasing Nottingham Forest at the Riverside Stadium.