Middlesbrough ran out deserved winners against nine-man Leeds thanks to a second-half goal from Marvin Emnes.
Both sides were reduced to 10 men when Leeds' Max Gradel and then Boro's Tony McMahon were dismissed for each collecting two yellow cards.
And Leeds were further up against it when skipper Jonny Howson was sent off when he felled Rhys Williams.
Justin Hoyte hit the woodwork for Boro before Emnes won it with his pinpoint shot into Andy Lonergan's top corner.
The home fans quickly redirected their anger at chairman Ken Bates who had been the target of a pre-match demonstration.
But Leeds were fortunate to only end the game one behind, with Lonergan twice saving well to deny Malaury Martin and Scott McDonald, and then making a stunning injury-time stop to keep out Julio Arca.