While obviously pleased at getting through to the next round of the Worthington Cup, he already has an eye on the visit of Steve Bruce's men on Saturday, and says: "The only downside on Tuesday was that we let ourselves down defensively, and that is something we have got to be worried about.
"We switched off and gave them a couple of chances - in the Premiership it would have cost matches, so it is something we have got to be aware of.
"But fair play to them - they forced a few decent saves.
"The performance was okay and in the first half we dominated the game.
"Possession-wise and chances-wise we battered them and we won, albeit on penalties, which is all that matters."
David was unable to save any of those Spireites' spot kicks on the night, but with one of them flashing past his post, he was able to appreciate Michael Carrick's decisive penalty going in, and quips: "The only excitement of the day was the penalties, wasn't it?!
"We worked on them in training in the morning and that was influential in the end.
"Lomy was a bit fortunate in the end with his - but it went in."
And he is keen to praise the hero of the night, Michael Carrick, adding: "He has been picked out by a select few for his performances but he has not been overly bad at all and has not even played every game.
"His penalty won the match on Tuesday, it was a steady performance against Chesterfield - as it was for all of us - and he was great against Chelsea."