January signing Matt Clarke's only previous goal in a Derby County shirt was in his loan spell with the Rams in January 2020
Derby County boosted their hopes of Championship survival as goals from Matt Clarke and Marcus Harness beat Frank Lampard's in-form Coventry City at a raucous Pride Park.
The Rams move to within a point of safety, after ending the Sky Blues' run of nine wins in 10 league games.
Clarke opened the scoring against the run of play on 23 minutes, stealing in at the far post to head home a teasing Harness right-wing free-kick.
Having set up the first, Harness then scored the second at the start of the second half, latching onto a loose clearance from Jerry Yates' cross to hammer in a left-foot volley from six yards.
After losing his first three games in charge, a second straight win for new Rams boss John Eustace completed a Derby season double over Coventry.
It was Derby's 2-1 win at the CBS Arena in November which triggered the following day's sacking of then boss Mark Robins - and the consequent appointment of former Rams, Chelsea and Everton boss Lampard.
Eustace's second straight win as Derby boss also meant that the Rams had won consecutive matches for the first time since September.
The Sky Blues started the stronger, as Ellis Simms and Victor Torp forced saves out of goalkeeper Jacob Widell Zetterstrom, while Clarke made an important block.
But the hosts broke the deadlock when Harness found January signing Clarke, who headed in only his second Derby goal - over five years on from his first, when he first joined the Rams on loan in January 2020.
Derby then secured victory just three minutes after the break through Ipswich loan man Harness - and Coventry offered little after that to end the run that has transformed them from Championship strugglers to play-off contenders.
Lampard's men drop a place to to sixth, two points ahead of seventh-placed Bristol City, who drew at Sheffield United.
Having moved to within a point of fourth-bottom Cardiff and Stoke City, Derby now wait on Wednesday's Stoke City-Blackburn Rovers game after Cardiff's home loss to second-bottom Luton. A Potters win would re-establish their four-point cushion over Derby above the relegation zone, before the Rams face Satuday's crucial trip to bottom club Plymouth Argyle.
Derby County head coach John Eustace told BBC Radio Derby:
"I'm very proud of the boys. The effort they put in was outstanding. The whole place was rocking. It was a group effort for sure.
"I know what this football club is all about. I left a club in the top six to come to a club with potential, and I know we can get to the Premier League with time.
"I wanted the lads to show the same attitude and desire we have seen since I arrived.
"We had a game plan. Luckily enough it came off. Now we've just got to keep believing in the process, and believing what we are doing."
Coventry City head coach Frank Lampard told BBC CWR:
"We couldn't keep winning as much as we have done. We played a team who were fighting, quite direct and focused on set-pieces.
"We got one wrong, gave them a goal, and something to hold on to, having had control of the game.
"The players tried to win, but they were just lacking a bit of conviction at the top end of the pitch, and that can happen.
"If that does happen, you don't want to be conceding those type of goals, which we had been pretty good at since I've come in."
