Maresca, the head coach who was appointed 18 months ago, parted company with Chelsea on New Year's Day.
They then lost defender Wesley Fofana to a virus, while first-choice goalkeeper Robert Sanchez was deemed not ready to play after injury.
Caretaker boss McFarlane had never led a senior men's match, and this first opportunity came against Guardiola, widely regarded as the best manager in the world, having overseen 1,011 games before this one and won a stack of trophies.
There would have been concern about whether Chelsea would be competitive at Etihad Stadium given such a disparity in experience between the men calling the shots from pitchside.
Chelsea quickly put those concerns to bed, pressing City high, causing havoc at set-pieces and remaining solid.
That was until they conceded during a poor spell at the end of the first half.
Nevertheless, supported by the unavailable Sanchez, Marc Cucurella, Levi Colwill and Moises Caicedo - who travelled to show solidarity - Chelsea presented as a united, competitive group capable of taking on City.
Of course, they were also found lacking at times, particularly with mistakes from Badiashile that led to the goal, and they were creatively short in the first half.
Then substitute Delap gave them a lift when he came on after the interval, pushing his team up the pitch, including one moment he created for himself in arguably his best league display since joining Chelsea.
Yet it was Fernandez who popped up with the equaliser - converting a low cross from the right for his seventh goal of the season, making him the joint-leading scorer for the Blues this season.
It was a worthy moment after an impressive effort from the squad and goes to show there is life left in Chelsea's season despite a chaotic episode that saw Maresca seemingly fall out with the hierarchy and ultimately leave.
Maresca's successor may turn out to be Strasbourg manager Liam Rosenior.
The new boss will inherit a team who sit fifth in the Premier League, just three points behind fourth-placed Liverpool, with opportunities to lead this group in the FA Cup third round, Carabao Cup semi-final and the Champions League.