Fernandes scored his scored 20th and 21st goals for Manchester United in their 4-1 win over Istanbul Basaksehir at Old Trafford on Tuesday night.
The Portuguese became the fastest Manchester United midfielder to surpass 20 goals and has 34 goal contributions in 35 games to his name since joining the club in the January transfer window.
In a brief period of time, Fernandes has emerged as the talisman at Old Trafford and Irwin admits that it is amazing that he keeps finding ways to leave his imprint on matches despite opposition defences paying extra attention to him.
The midfielder has also been accused of losing possession as well, but the former defender is delighted that Fernandes takes risks and feels any team need a player of that ilk.
Asked if Fernandes is the most important player at Manchester United at the moment, Irwin told MUTV: “I don’t think there is any doubt about that.
“Since he came here he started scoring goals straight away, and he has kept it going.
“He is one of those where you are thinking defenders, midfielders, surely the opposition will pick him up somehow, but he keeps finding those spaces.
“He is just a breath of fresh air to us.
“He is a really risky player in what he does, but you need somebody like that in your team.”
Fernandes was taken off at the hour mark on Tuesday night and is almost certain to start against Southampton on Sunday.