There were more errors and a few signs of promise from Tomori who was good on the ball and strong in the tackle but perhaps a little too eager to impress after that early blunder, often rushing into areas that left his more experienced - and slow - centre-back partner Keogh exposed.
Ahead of kickoff, banners with the words "GOAL AFTER GOAL, GAME AFTER GAME" and "FOREVER A BLUE, ALWAYS A LEGEND" flanked a giant image of Lampard in the Matthew Harding Stand, emblazoned with the number 211 - his peerless goal tally for Chelsea. Yet, as an opposition manager and even in narrow defeat, he will have purred at the performance delivered by his Derby County team in surroundings so familiar.
It was every bit as "special" as Lampard had predicted, but also slightly surreal.
"I respect this club, I don't have to talk about this club".
Lampard took it all in his stride, of course, transitioning effortlessly from clapping the songs directed at him to vigorously applauding his Derby players as they hassled and harried Chelsea into defensive mistakes. I've got no bad feelings and I've got great relationships. But I walked in the front door here and got that.
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"My overriding feeling is thanks to the Chelsea fans and the Derby fans and pride at the team". So he was asked 'Do you want to work?', 'How hard can you work?' And he did that. "To deal with that, with all eyes on him at Chelsea, at his parent club, his recovery under that pressure was brilliant".
Chelsea assistant and Lampard's former team-mate Zola was frustrated with the Blues' defensive efforts, but did concede that much of that was down to Derby's play. He was one of the first players I analysed and I said 'this player is for us'.
Ruben Loftus-Cheek is now enjoying the best goalscoring spell of his career, netting in two consecutive games for the first time.
Summing up the Carabao Cup run this season, Lampard said: "It was good from the beginning to the end; Oldham, Hull, obviously Old Trafford, and then to perform like that here tonight, people are watching that so we have set our standards".
A Mount shot went narrowly wide off Cahill as Derby went close again. But now they have gone out and they can concentrate on the Championship, which is what is so important now.
Part of the Blues' success has seen a small rise in the careers of English duo Ross Barkley and Ruben Loftus-Cheek, both of whom are thriving under Sarri in the Italian's left-sided midfield role, carrying some of the attacking burden of the team.