Michael Carrick's Red Devils increased their stranglehold on third place with a hard-fought Old Trafford triumph against Keith Andrews' Bees on Monday (Tuesday AEST), giving them an 11-point lead over sixth-placed Brighton & Hove Albion with just four matches to play.
Fernandes has been integral to United's rise and impeding return to Europe, with the skipper setting up a 19th goal of the campaign as Benjamin Sesko scored after Brazil international Casemiro continued his memorable farewell tour with a headed opener.
The Portuguese playmaker is now just one shy of the record 20-assist tally in a single season shared by Kevin De Bruyne and Thierry Henry.
Fernandes' latest contribution helped settle nerves after unusually wasteful Igor Thiago threatened to level in an entertaining first half.
United teenager Kobbie Mainoo showed incredible balance, footwork and awareness inside the opening minutes to wriggle free and pass to Amad Diallo, whose shot Sepp van den Berg blocked on the line.
Brentford goalkeeper Caoimhin Kelleher clawed away a thumping Harry Maguire header from a Fernandes cross, and the United pair soon played a vital role in the opener.
The captain's deep 11th-minute corner was headed back across goal by returning defender Maguire to the back post, where Casemiro showed strength to nod home.
The Bees fell behind for the first time since February and were two down after 43 minutes.
A powerful Amad challenge started a counter-attack as Fernandes took the ball over the halfway line and beyond, keeping his cool before passing for Sesko to score having shown similar composure.
Maguire was denied by Kelleher when the second half got underway and man of the match Casemiro whizzed a low long-range effort narrowly wide.
The visitors pushed and Dango Ouattara hit a post before Mathias Jensen's long-range effort with three minutes to go, but Carrick's side held out for a win that keeps them on course for Champions League football.
