Debutant Alex Nimely scored one goal and made two as rock-bottom Coventry inflicted a third straight league defeat on nine-man Middlesbrough.
Nimely, who spent the first half of the season on loan with Boro, set up Gary McSheffrey's 15-yard opener.
Boro had Kevin Thomson sent off for a second yellow card before Nimely's header made it 2-0 and Matthew Bates put through his own net for the third.
Scott McDonald's header gave Boro hope but Julio Arca saw red for a lunge.
The visitors can have no complaints about Arca's dismissal after the midfielder went in two-footed on Sammy Clingan.
But the first-half dismissal of Thomson was a little harsh on the visitors and undoubtedly changed the course of the game, even though the hosts were already leading courtesy of McSheffrey's finish from inside the box.
Thomson was harshly booked for bringing down Cyrus Christie and then saw red for getting a second caution for a studs-up challenge on McSheffrey.
Nimely made the one-man advantage count after the break, heading Coventry's second.
And Bates then scored at the wrong end on 64 minutes after a clever cross from substitute David Bell to seemingly end Boro's chances.
Boro responded instantly when a Marvin Emnes cross was nodded in by McDonald.
But Coventry held out with relative ease and Boro's misery was complete when Arca earned their second red card.