Middlesbrough relinquished control of the top of the Championship after succumbing to a frustrating 1-0 defeat at home to in-form Leeds United in the day's early kickoff.
Alex Mowatt's early goal with the aid of a deflection from the edge of the area was enough to settle the encounter, with the hosts unable to capitalise on a host of chances in either half.
With goalkeeper Dimi Konstantopoulos suspended following a red card in a midweek draw at Birmingham, cup keeper Tomas Mejias returned to the starting eleven. Czech defender Tomas Kalas started alongside Ben Gibson at the back, but fellow Chelsea loanee Patrick Bamford settled for a spot on the bench.
For the visitors, top scorers Mirco Antenucci was on the bench while seven-goal Souleymane Doukara missed out completely. Marco Silvestri was between the sticks for a side otherwise unchanged from their recent win at home to Millwall, in which Mowatt also scored the only goal.
For a minor Yorkshire derby, the atmosphere ahead of kickoff was good with both sets of fans in fine voice amidst a crowd of over 25,000. Middlesbrough's raucous South Stand 'ultras' ramped up the palpable tension in the stadium by poking fun at Leeds' controversial owner Massimo Cellino, displaying a banner of their own owner Steve Gibson and the phrase 'Fit and Proper'.
However, their glee was short-lived as the visitors stunned the home crowd with a shock early opener. Following a poor throw from keeper Mejias, Lewis Cook played the ball to Mowatt and a deflection on his low shot took the ball just inside the bottom left corner.
Boro almost hit back immediately after a well-worked free kick routine, but Belgium striker Jelle Vossen missed his kick as he looked to sweep the ball past Leeds keeper Silvestri, while Kike had an effort saved after bustling past a defender.
Former Leeds midfielder Adam Clayton came closest for the hosts in a half which they utterly dominated, his looping deflected shot seemingly goal-bound before an acrobatic stop from the impressive Silvestri.
Top-scoring captain Grant Leadbitter shot wide and, while Leeds occasionally threatened on the break, the story of the first half was one of exasperation for the home crowd as their side piled forwards without ever managing to apply the final touch.
The two sides came out unchanged for the second half and Leeds threatened a repeat of the first, Scott Wootton inches away from doubling their advantage as his header cannoned off the top of the crossbar in the opening exchanges. The visitors took more of a foothold in the game in the second half and began to retain possession, while captain Sol Bamba also headed wide from close range.
It was not long until Aitor Karanka decided to turn the screw, bringing on Bamford and the Championship's Player of the Month for January in Lee Tomlin. However, if anything, the changes worked against Boro as Leeds' threat on the counter became more palpable and their own chances began to dwindle. Albert Adomah remained the most likely to make something happen, but was unable to find the final ball despite controlling the right wing.
The introduction of former Everton man Adam Forshaw proved a mistake for the home side as the midfielder was booked seconds after coming on, before the rest of his team had to finish the match with ten men. Following a clash of heads in the middle of the park, the counter-attacking Vossen lay worryingly static in the centre circle and was eventually stretchered off after some seven or eight minutes of treatment.
Tensions continued to flare as the match wore into its nine minutes of stoppage time, with Kalas and Rodolph Austin squaring up after a clear foul at the Boro end. Moments later, the Leeds midfielder stung the palms of Mejias with a rasping drive from some 30 yards which needed to be tipped over the bar.
The Boro goalkeeper soon saw the chance for a moment of glory as he made his way up the field for a 98th-minute corner but, like 17 others, it came to nothing and the away contingent of 2,700 erupted on the cue of the final whistle.
It was the home side's first defeat in the league since the 20th of December and their first at the Riverside Stadium since way back in August, but Leeds moved into the top half of the table with their fifth win in six.