Anthony Knockaert inspired a second-half Leicester comeback to hand a first away defeat of the season to local rivals Derby in the Capital One Cup.
After Derby's Jake Buxton had an early header cleared off the line, the Rams took the lead as Chris Martin scuffed a shot past Kasper Schmeichel.
Three-time League Cup winners Leicester improved with substitute Knockaert scoring a 25-yard free-kick.
Danny Drinkwater grabbed the winner for the hosts with a backheel finish.
The victory denied Derby a first win in Leicester for over a decade and with the visitors on top for most of the game, it was Knockaert's introduction after 63 minutes that changed the course of the match.
Derby's last win at Leicester - a 3-0 triumph - was in the Premier League at Filbert Street in February 2002
His superb free-kick levelled matters and he had a hand in Drinkwater's decisive strike nine minutes from time.
Nigel Pearson made eight changes to his side, who are third in the Championship, almost went ahead in the first minute when Derby's Kieron Freeman had to clear the ball off his own line from a Tom Hopper header.
Nigel Clough's Derby side then created the best of the chances before good work inside the box from Johnny Russell set up Martin's opener.
Pearson brought on David Nugent and Lloyd Dyer after the break to try to give his side some added zest but it was Knockaert's arrival was the one that made the difference.
Defeat was cruel for Derby for as the substitute crashed his free-kick in off the bar and three minutes later another Knockaert set-piece found the net via a couple of deflections with the final touch coming off Drinkwater.
Leicester manager Nigel Pearson on forward Anthony Knockaert:
"We know he's a talented player. I can't remember too many shots he's had like that hitting the target, so well done to him.
"He still has a lot to learn but he's come on leaps and bounds in the 14 months we've had him.
"It's good to get through, that was the aim at the start of the night. The performance was a mixed bag, but that happens when you make so many changes. But I expected that lack of fluency a little, although I wanted us to show a little more impetus."
Derby boss Nigel Clough:
"We felt we'd done enough to win the game throughout the 90 minutes, certainly in the first half.
"It was an excellent away performance and the one-goal lead was not sufficient reward for how we played.
"With 10-15 minutes to go we are relatively comfortable and I don't think Lee Grant has had anything to do during the game up to that point. They were both needless free-kicks to give away so we feel we've contributed to our own downfall there."
Live Text Commentary
Full Time The game is over, as the referee blows the whistle.89:59 Substitution
Substitution Michael Jacobs on for Will Hughes.87:33
Johnny Russell takes a weak shot and went wide left of the net.85:41
Jake Buxton takes a shot. Kasper Schmeichel catches the ball.85:27
Craig Bryson takes the free kick.85:17
Unfair challenge on Jake Buxton by Anthony Knockaert results in a free kick.84:50
Ben Davies restarts play with the free kick.84:39
Free kick awarded for an unfair challenge on Will Hughes by Ignasi Miquel.81:52
Free kick taken by Ben Davies.80:42
Assist on the goal came from Matty James.80:42 Goal scored
Goal! - Danny Drinkwater - Leicester 2 - 1 Derby Danny Drinkwater slots the ball right footed into the goal. Leicester 2-1 Derby.80:04
Free kick taken by Matty James.79:59
Dean Hammond fouled by Ben Davies, the ref awards a free kick.77:19 Goal scored
Goal! - Anthony Knockaert - Leicester 1 - 1 Derby Anthony Knockaert finds the net with a shot from the free kick. Leicester 1-1 Derby.76:35
Conor Sammon concedes a free kick for a foul on Dean Hammond.75:39
Johnny Russell has an effort at goal and missed to the right of the net.72:56
Free kick taken by Jake Buxton.72:45
Free kick awarded for an unfair challenge on Johnny Russell by Jeff Schlupp.71:33
Jake Buxton restarts play with the free kick.71:24
Ben Davies fouled by Dean Hammond, the ref awards a free kick.
Clearance by Craig Forsyth.69:09
Corner taken by Matty James from the left by-line.67:30
The ball is delivered by Jeff Schlupp.66:47
Danny Drinkwater takes a brilliant shot and went wide left of the goal.66:27
Richard Keogh manages to make a clearance.65:03
Shot by Craig Forsyth went wide right of the target.64:10
The ball is crossed by Lloyd Dyer.62:36
Kieron Freeman crosses the ball in from the free kick.62:31
Free kick awarded for an unfair challenge on Johnny Russell by Jeff Schlupp.62:14 Substitution
Substitution (Leicester) makes a substitution, with Anthony Knockaert coming on for Gary Taylor-Fletcher.60:46
Free kick taken by Kasper Schmeichel.60:42
The referee blows for offside against Johnny Russell.59:51
Lee Grant restarts play with the free kick.59:40
Will Hughes fouled by Jeff Schlupp, the ref awards a free kick.59:03
Free kick taken by Liam Moore.58:56
Unfair challenge on Gary Taylor-Fletcher by Conor Sammon results in a free kick.55:16
Lee Grant takes the free kick.54:57
The referee blows for offside.51:46
Lee Grant restarts play with the free kick.51:31
Kieron Freeman fouled by David Nugent, the ref awards a free kick.51:10
David Nugent has an effort at goal.49:56
Matty James takes the free kick.49:46
Dean Hammond fouled by Will Hughes, the ref awards a free kick.49:30
Richard Keogh manages to make a clearance.47:00
Conor Sammon makes a clearance.46:52
Danny Drinkwater takes the free kick.46:28
Kieron Freeman goes into the book for unsporting behaviour.46:28 Booking
Foul by Kieron Freeman on Lloyd Dyer, free kick awarded.45:48
Ben Davies sends in a cross.45:01
The second half begins.45:01 Substitution
Substitution David Nugent is brought on as a substitute for Tom Hopper.45:01 Substitution
Substitution Lloyd Dyer on for Zoumana Bakayogo.45:00 +3:38 Half time
Half Time It is the end of the first-half.45:00 +3:10
Jake Buxton restarts play with the free kick.45:00 +2:58
Dean Hammond booked for unsporting behaviour.45:00 +2:58 Booking
Unfair challenge on Will Hughes by Dean Hammond results in a free kick.45:00 +1:02
Danny Drinkwater takes the free kick.45:00 +0:56
Free kick awarded for a foul by Craig Forsyth on Liam Moore.42:50
Shot by Ben Davies cleared the target.41:54 Goal scored
Goal! - Chris Martin - Leicester 0 - 1 Derby Chris Martin scores with their right foot. Leicester 0-1 Derby.40:49
Free kick taken by Lee Grant.40:42
Foul by Tom Hopper on Craig Bryson, free kick awarded.39:37
Clearance made by Marcin Wasilewski.39:34
The ball is swung over by Craig Forsyth.38:16
Corner taken by Ben Davies from the right by-line.35:52
The ball is delivered by Ben Davies.35:06
Ben Davies has an effort at goal. Kasper Schmeichel catches the ball.33:11
Shot by Danny Drinkwater cleared the crossbar.29:24
Jake Buxton takes the free kick.29:04
The assistant referee flags for offside against Dean Hammond.28:47
Kasper Schmeichel restarts play with the free kick.28:44
Craig Bryson is caught offside.27:22 Substitution
Substitution Ben Davies joins the action as a substitute, replacing Paul Coutts.24:43
Paul Coutts is penalised for handball and concedes a free kick.18:16
Free kick taken by Jake Buxton.18:14
The referee blows for offside.17:03
Tom Hopper gets a header at goal. Lee Grant catches the ball.15:50
Zoumana Bakayogo makes a clearance.15:48
Free kick taken by Will Hughes.15:06
Free kick awarded for a foul by Dean Hammond on Craig Bryson.14:20
Zoumana Bakayogo crosses the ball.13:17
Kieron Freeman delivers the ball.11:02
Shot by Craig Bryson. Parried by Kasper Schmeichel back into danger.10:06
Johnny Russell takes a shot. Kasper Schmeichel safely holds on.9:07
Will Hughes makes a clearance.8:49
Corner from the left by-line taken by Matty James.8:26
Jake Buxton gets a header at goal.8:04
Corner taken by Paul Coutts.4:19
Jake Buxton takes the free kick.4:13
Jeff Schlupp is flagged offside by the assistant referee.3:31
Shot by Dean Hammond went wide of the right-hand upright.2:10
Shot by Will Hughes. A parry by Kasper Schmeichel prevents the goal.1:16
Richard Keogh takes the free kick.1:11
Free kick awarded for a foul by Jeff Schlupp on Richard Keogh.0:44
Zoumana Bakayogo takes a shot.0:00
The match has kicked off.
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