Match ends, Chelsea 3, Derby County 2.
Chelsea knocked out Derby in the Carabao Cup fourth round as Frank Lampard's return to Stamford Bridge as a manager ended in dramatic defeat.
Five goals were scored in a frantic first half, including two own goals from Derby defenders Fikayo Tomori and Richard Keogh.
Derby came from behind twice through Jack Marriott and Martyn Waghorn.
But Cesc Fabregas slotted home four minutes before half-time for what proved to be the winner.
Derby substitute David Nugent hit the inside of the post with a minute of normal time remaining but it rebounded safely into goalkeeper Willy Caballero's hands.
It was the worst start possible for 20-year-old Chelsea loannee Tomori, facing his parent club, who missed when attempting to clear Davide Zappacosta's low cross, and saw the ball deflect backwards off his standing leg and into the net.
Derby striker Marriott levelled with his fourth goal in five games after Tom Huddlestone pounced on a poor pass and a slip by Chelsea centre-back Gary Cahill.
The hosts were ahead again 12 minutes later when Zappacosta's cross was again deflected into the goal by Derby captain Keogh.
Then Waghorn - who had earlier missed a chance to make it 2-1 from Marriott's through ball - equalised again for Derby by tapping in Mason Mount's low cross.
Chelsea right-back Zappacosta was involved in another goal when the ball ricocheted kindly from him for Fabregas to make it 3-2.
Derby had chances in the second half as Mount, Marriott and Keogh came close, while Chelsea's Cahill was denied from close range and Alvaro Morata had a header saved by keeper Scott Carson.
Before kick-off, a minute's applause was held in tribute to the victims of the Saturday's helicopter crash at Leicester City. Former Foxes boss Claudio Ranieri - who managed Chelsea from 2000 to 2004 - was at Stamford Bridge.
More to follow.
Match ends, Chelsea 3, Derby County 2.
Second Half ends, Chelsea 3, Derby County 2.
Richard Keogh (Derby County) is shown the yellow card for a bad foul.
N'Golo Kanté (Chelsea) wins a free kick in the attacking half.
Foul by Richard Keogh (Derby County).
Willian (Chelsea) wins a free kick on the left wing.
Foul by Tom Huddlestone (Derby County).
David Nugent (Derby County) hits the left post with a right footed shot from the right side of the box. Assisted by Jack Marriott with a through ball.
Attempt saved. Jack Marriott (Derby County) right footed shot from the right side of the box is saved in the bottom right corner. Assisted by Jayden Bogle.
Attempt saved. Mason Mount (Derby County) right footed shot from outside the box is saved in the bottom left corner. Assisted by Richard Keogh.
Attempt saved. Richard Keogh (Derby County) right footed shot from the centre of the box is saved in the centre of the goal. Assisted by Jayden Bogle with a through ball.
Emerson (Chelsea) is shown the yellow card for a bad foul.
Foul by Emerson (Chelsea).
Jayden Bogle (Derby County) wins a free kick on the right wing.
Substitution, Derby County. David Nugent replaces Harry Wilson.
Substitution, Derby County. Craig Forsyth replaces Scott Malone.
Foul by David Luiz (Chelsea).
Scott Malone (Derby County) wins a free kick in the defensive half.
Corner, Chelsea. Conceded by Scott Carson.
Attempt saved. Álvaro Morata (Chelsea) header from the centre of the box is saved in the bottom right corner. Assisted by Willian with a cross.
Corner, Chelsea. Conceded by Fikayo Tomori.
Attempt missed. Álvaro Morata (Chelsea) header from the left side of the six yard box misses to the right. Assisted by Emerson with a cross.
Mateo Kovacic (Chelsea) wins a free kick in the attacking half.
Foul by Tom Lawrence (Derby County).
Substitution, Chelsea. César Azpilicueta replaces Davide Zappacosta.
Attempt missed. Álvaro Morata (Chelsea) header from the centre of the box misses to the left. Assisted by Davide Zappacosta with a cross.
Pedro (Chelsea) wins a free kick in the defensive half.
Foul by Scott Malone (Derby County).
Foul by Emerson (Chelsea).
Mason Bennett (Derby County) wins a free kick on the right wing.
Attempt blocked. Willian (Chelsea) right footed shot from outside the box is blocked. Assisted by Pedro.
Corner, Derby County. Conceded by Gary Cahill.
Attempt blocked. Mason Mount (Derby County) right footed shot from outside the box is blocked. Assisted by Fikayo Tomori.
Substitution, Chelsea. Pedro replaces Ruben Loftus-Cheek.
Corner, Derby County. Conceded by Willy Caballero.
Attempt saved. Jack Marriott (Derby County) right footed shot from the right side of the box is saved in the centre of the goal. Assisted by Tom Huddlestone with a through ball.
Substitution, Chelsea. David Luiz replaces Andreas Christensen.
Ruben Loftus-Cheek (Chelsea) wins a free kick in the defensive half.
Foul by Fikayo Tomori (Derby County).
Corner, Derby County. Conceded by Andreas Christensen.