You would not have known which side had been a non‑league outfit just two and a half years ago from watching the first 45 minutes.
Chelsea made nine changes, leaving Cole Palmer, Moises Caicedo and Enzo Fernandez out entirely, with Marc Cucurella, Reece James and Joao Pedro among the substitutes.
On the pitch, Chelsea started with five defenders, two defensive midfielders and only three natural attackers – and it showed.
They did not register an attacking action of note until defender Jorrel Hato, playing out of position as an attacking midfielder, floated a poor cross into the arms of the Wrexham goalkeeper.
Alejandro Garnacho took 27 minutes to produce Chelsea's first shot, tame as it was, while the equaliser in the 40th minute came firmly against the run of play.
It was a far cry from the quality on display at Aston Villa in midweek, as Chelsea tried – and failed – to rotate their squad effectively.
It leaves the question of whether Chelsea underestimated Wrexham with Paris St‑Germain looming in the Champions League, or whether their second string simply falls well short of the level required.
Of course, the quality from the bench eventually told, while Dobson's red card took the wind out of the Championship club's sails despite them coming close to equalising in the second half of extra time.
Questions remain for Liam Rosenior – who is encouraged by the hierarchy to rotate – and about Chelsea's wider approach.
Should they really be averaging five changes per match, avoiding the use of the same back four in consecutive games since appointing their new manager, or even rotating their goalkeepers Robert Sanchez and Filip Jorgensen at this stage?
