Derby, who are coached by Chelsea legend Lampard, went behind when Tomori inadvertently deflected a cross into his own net.
The encounter had produced four goals within the first half-hour and there was more to come when Cesc Fabregas scored the goal that proved to be the difference between the two sides towards the end of the first half.
Chelsea dumped Frank Lampard's Derby out of the League Cup despite a valiant effort by the Championship side to battle back from a defensive Halloween horror show.
The visitors made several changes after losing to Manchester City in the Premier League at Wembley 48 hours earlier but managed to carve out a two-goal lead through South Korean Son.
For this reasons, we chose to compile a list of key players that have made the defense of these football clubs hard to penetrate.
It was a special night for the manager who returned to Stamford Bridge for the first time tonight as a manager. Marriott slips through Nugent and his shot from an acute angle beats Caballero but cannons off the post and bounces back to into the safe arms of the Chelsea goalkeeper.More news: Statue of Unity Interesting facts about the world s tallest statue
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DF David Luiz, 6 - Brought on for Christensen to give Chelsea greater defensive solidity, he broadly did his job as Derby pushed in vain for an equaliser in the final 20 minutes.
Redknapp was also full of praise for Chelsea loanees Mason Mount and Tomori, particularly with the way the latter responded after scoring a disastrous own goal after five minutes. Subs: Forsyth 5, Bennett 5, Nugent 6. His forward runs were just as risky to Chelsea as to the opponents; both visiting goals came from the space vacated on his flank.
And it is this game from which Derby can gain confidence, with the Blues switching off defensively at times.
Coming only a matter of days after Lampard was left fuming after Jayden Bogle scored an equally ridiculous own-goal, this Tomori one will take some beating. "So we didn't have control of the game".
Chelsea are still unbeaten in domestic competition this season, and despite their potential absentees they will be looking to come through against Derby and move into the quarter final of the competition. He offered plenty of bite and might even have provided a lead with a cleverly clipped pass which freed Martyn Waghorn, only for the lumbering No 9 to panic in front of goal and stumble as he poked a shot straight at Caballero.
"There wasn't a tear in the eye, but it was emotional, " Lampard said.
With rotation likely, Loftus-Cheek will be one of the favourites to start for Chelsea and could yet again find the net.