McClaren, whose previous spell in charge started with a 3-1 victory against Leeds in 2013, watched Johnny Russell settled a tight Championship clash with a 57th-minute strike.
Russell scored just five minutes after coming off the bench, pouncing on the scraps from a corner to hammer a shot under United goalkeeper Rob Green.
Leeds had earlier hit the crossbar through Kyle Bartley and Marcus Antonsson struck a post in the dying seconds as United piled on the pressure.
Head coach Garry Monk - serving a one-game touchline ban - was left to rue that moment as Derby claimed three points.
Monk made one change to his starting line-up, replacing the injured Stuart Dallas with Alex Mowatt.
Dallas failed to recover from a thigh strain suffered on international duty with Northern Ireland and he made way for Mowatt as Monk stuck with his favoured 4-2-3-1 formation at the iPro.
Mowatt’s start was his first in the league since a 1-0 defeat to Huddersfield Town at the start of last month, with Leeds looking to maintain their form after five wins in seven games.
McClaren also made one switch with Max Lowe replacing Marcus Olsson, and Derby controlled the first half without truly stretching Leeds.
Former United midfielder Bradley Johnson pinged an early shot over the crossbar from long range but Bartley and Pontus Jansson dealt well with the threat of Derby’s lone striker, Matej Vydra, and Leeds went close when Chris Wood headed Luke Ayling’s cross wide on 28 minutes.
County threatened themselves soon after as Vydra anticipated Johnson’s chipped pass and volleyed past Rob Green’s far post but despite struggling before the break, Leeds should have opened the scoring in injury-time.
Mowatt laid on a free header for Bartley with a corner into the box but the defender spared County by smashing the ball off Scott Carson’s crossbar.
Derby appeared to suffer a blow early in the second half when Bartley’s tackle on Anya forced the winger to limp from the field but Russell, his replacement, broke the deadlock just five minutes later.
The Scot ran into smash home a low shot after a Tom Ince corner was scrambled to the edge of United’s box.
Green then dived to push wide an effort from Will Hughes as Derby tried to kill the game and the linesman came to Leeds’ rescue on 69 minutes when he flagged for offside as Vydra turned home Ince’s low pass.
Leeds fought for an equaliser and Kalvin Phillips was denied when Carson dived to parry his late free-kick.
Bartley could also have snatched a point but his injury-time volley flew into Carson’s hands and substitute Antonsson watched a curling shot rattle a post at the death.
Monk was frustrated not to get anything from the game.“I said to the players at half-time that we need to put our game on the pitch a little bit better and we came out and we started to do that and then we conceded a poor goal from our point of view which put us on the back foot,” he said.
“We had a go in the last 25 minutes and had a couple of chances but overall I think we didn’t do enough of the things we have done really well in recent games with the ball to give ourselves the best chance of getting something.
“We probably deserved something from the game but it’s one of those where you probably can’t complain that you didn’t. We didn’t do enough of the good things that we have been doing recently to really carve them open or create really clear opportunities.
“We hit the woodwork a couple of times and were probably the wrong side of those margins but the pleasing thing for me is we are still very competitive in games and were fighting for the result right up to the very end.”
Derby County: Carson, Christie, Keogh, Pearce, Lowe, Butterfield (Bryson 75), Johnson, Hughes (Baird 84), Ince, Vydra, Anya (Russell 52). Subs (not used): Mitchell, Bent, Wilson, Weimann.
Leeds United: Green, Ayling, Bartley, Jansson, Taylor, Phillips, O’Kane, Hernandez, Mowatt (Grimes 80), Sacko (Roofe 59), Wood (Antonsson 83). Subs (not used): Silvestri, Coyle, Cooper, Vieira.
Read more at: http://www.yorkshirepost.co.uk/sport/football/leeds-united/what-garry-monk-makes-of-leeds-united-s-1-0-defeat-at-derby-1-8183226