Jack Marriott equalised early in the game following Fikayo Tomori's fifth minute own goal.
Nevertheless, of the two, it is Mount who can be more pleased with his performance, leaving Stamford Bridge with an assist - a wonderfully weighted cross for Martyn Waghorn to score Derby's second - and several knowing nods of approval from the home faithful as he twisted and turned away from pressure and fizzed the ball left and right from his advanced spot in midfield.
This fourth-round clash provided an opportunity to do so and Lampard was serenaded throughout by Chelsea supporters, and he responded by acknowledging them and the Derby fans at the end.
But he grew into the game and made good challenges and good decisions.
A penalty shootout win over Manchester United - managed by Lampard's former mentor at Chelsea, Jose Mourinho - set up the tie at the Rams boss' former stomping ground.
It will not be an easy task however, for the Rams to grab a second Premier League scalp given Chelsea's impressive start to the season under Maurizio Sarri. 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.
Attack: Chelsea are set to be without Eden Hazard once again as the Belgian worldwide is still nursing a back injury that's seen him miss the last two games.
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"This wasn't a game for Mason to run because he's against Chelsea, against [N'Golo] Kante, [Mateo] Kovavic and Fabregas", Lampard added.
The Belgian forward has also won two League Cups, the FA Cup and the Europa League during his six-season stint at Stamford Bridge following a move from Lille in 2012. Subs: Forsyth 5, Bennett 5, Nugent 6.
Key Stat: Chelsea have conceded three goals in their past three matches across all competitions. However, the Blues are confident Hazard will be fit to return against Palace at the weekend.
Lampard scored a club record 211 goals in 648 appearances and 13 years at Chelsea, but left when his contract expired in June 2014 without having the chance to say goodbye. "So we didn't have control of the game".
Yet for all their slick approach play, Derby's defence was constantly on edge, particularly with Ruben Loftus-Cheek at his rampaging best.
Perhaps that was everything, but it was hard not to link Chelsea's fluctuating concentration levels with the fact that the focus of Stamford Bridge so often drifted to the visiting dugout.
"His character was vast", Lampard said of Tomori.