Manchester United's past five fixtures have produced a total of 27 goals
With the visitors taking the lead twice, Erik ten Hag's side were staring at a humiliating loss to a side who have won just three times this season.
But Fernandes levelled from the penalty spot before driving Manchester United in front from 25 yards nine minutes from time.
The Portuguese created a first goal since February for striker Rasmus Hojlund four minutes later to move his side up to sixth spot and earn praise from his manager.
"He showed his leadership," said Ten Hag.
"He tried to encourage the team and he is also in good form. We put him in the right position and when he is there, he makes the right decisions.
"He can create a lot, score, assist and make key actions. We are very happy with his performance and his attitude."
Fernandes has now scored seven goals and collected two assists in Manchester United's past five games.
In total, there have been 27 goals in that period. Manchester United have conceded and scored at least two in all of those games.
In entertainment terms, it is sensational. However, there is zero sense of structure and it can only be wondered what new technical director Jason Wilcox made of it as he watched from the Old Trafford directors' box for the first time since his appointment was confirmed last week.
Ten Hag had railed against the media the day before the game, labelling critical coverage of his side's FA Cup semi-final victory on penalties over Coventry "embarrassing" and "a disgrace" - but his team failed to follow up by convincing on the pitch.
Without a win since February, Sheffield United led twice, through Jayden Bogle in the first-half and Ben Brereton Diaz in the second.
Harry Maguire's deft header pulled the home side level on the first occasion, before Fernandes took control.
-- Courtesy of BBC Sport