Man City headed into Sunday’s Etihad clash 14 points clear of their rivals and off the back of a 21-game winning run across all competitions.
Ole Gunnar Solskjaer’s Red Devils, meanwhile, went into the game having drawn their last three games 0-0 - but it took less than two minutes for United to find the net in the derby.
Gabriel Jesus clumsily fouled Anthony Martial in the City penalty area, and Fernandes - who defended his record against the ‘Big Six’ before the game - duly delivered from the spot as Ederson couldn’t keep out his low effort.
That early goal suited United’s counter-attacking approach to a tee, with Dean Henderson - starting in goal again with David De Gea in Spain following the birth of his child - rarely troubled by the table-toppers as they went into the break ahead.
United hit City with another sucker-punch soon after the restart, with Henderson starting a counter for Shaw to play a one-two with Marcus Rashford before clinically finishing to double the visitors’ lead 50 minutes in.
City had a host of half-chances to get back into the game - including one great opening for Raheem Sterling - but United were well worth their win, with an injury for Marcus Rashford the one sour note for Solskjaer.
While the result may have little bearing on the title race given City still lead United by 11 points, it was a reminder for Pep Guardiola’s side that their neighbours are not quite done yet.
The win was also a huge boost for United in the context of the top four race, sending them second again and giving Solskjaer’s men some breathing space.