Fernandes scored a penalty after just two minutes at the Etihad Stadium and Shaw added the second on 50 minutes as United inflicted a first defeat on their rivals since November.
The result cut City’s lead over United at the top of the Premier League to 11 points and, while it may be a stretch to suggest the title race has been reignited, it has slowed what was looking like a procession.
It may certainly rejuvenate United, who might have feared being dragged into a battle for a top-four place after an indifferent series of performances.
City were unable to force their way back into the game allowing United, for now at least, the local bragging rights.
The only downside for the visitors was the loss of the inspirational Marcus Rashford through injury in the second half.