Derby claimed a narrow 1-0 victory at the Ricoh Arena that all but secures their Coca-Cola Championship status and effectively ends Coventry's faint hopes of gatecrashing the play-off places.
Centre-back Shaun Barker grabbed the only goal of the game in the 20th minute - his finish from Michael Tonge's corner adjudged to have crossed the line - to send the Rams past the 50-point mark generally considered enough to avoid relegation.
Nigel Clough's in-form side, who extended their unbeaten run to five games with only their third away win of the season, are now eight points clear of third-bottom Crystal Palace with five games remaining.
In fact, Barker's fifth goal of the season moved County to within one point of their midlands neighbours - who have seen their play-off dreams shattered by a six-match winless streak.
But there was controversy with almost the last kick of the game as the Sky Blues were denied a stoppage-time equaliser, with the Ricoh celebrating, when substitute Chris Hussey's effort was ruled out for offside following a lengthy chat between referee Andy D'Urso and his assistant.
Former Rams loanee Jonathan Stead wasted no time making his presence felt, turning neatly before firing narrowly wide after just 20 seconds.
Strike partner Clinton Morrison was next to try his luck with merely two minutes gone, but Stephen Bywater saved comfortably before Stead again tested the Derby keeper.
The Sky Blues started firmly on the front foot and were looking menacing in the final third, with the lively Stead enjoying his third effort of the afternoon with just 10 minutes on the clock.
But with Keiren Westwood yet to make a save, Derby stunned the home support at the Ricoh Arena by taking the lead.
Tonge's corner was flicked on at the near post by the recalled Rob Hulse and Barker met the ball with a left-footed effort from eight yards that was, according to the referee's assistant, hooked away from behind the line.
The balance of play certainly levelled out after Derby's breakthrough, although Bywater again saved from Stead as the on-loan Ipswich forward looked to head Coventry level.
And while the clash had turned into a somewhat scrappy affair over the second quarter of the game, the visitors were posing much more of a threat in attack despite struggling with the quality of their final ball.
Coventry midfielder Carl Baker showed his ability to strike the ball cleanly in the first half and Bywater did well to parry his stinging effort to safety at the start of the second.
Hulse scuffed off target almost immediately when in a good position at the other end but it was the hosts who, in similar fashion to the first half, flew out of the blocks.
Yet a combination of stout defending and weak finishing preserved Derby's advantage as, like in the first 10 minutes, the visitors weathered the storm before coming back into it themselves.
Sky Blues boss Chris Coleman made a double substitution as the game entered the final 20 minutes in a bid to inject some fresh impetus.
And it was Hussey who looked to have salvaged a late point for the hosts in injury time but his strike was ruled out for offside, leaving Coventry goalless for the first time in 11 home league games.
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