Right at the start of the match at Old Trafford, the visitors scored what will go down as one of the most bizarre goals in Premier League history.
Emile Smith Rowe fired the ball into the back of the net after United cleared a corner, despite the fact David De Gea was down injured virtually on the goalline.
It looked as if the strike from Arsenal's young sensation would be chalked off, until it was revealed that the De Gea was fouled by his own man Fred, who unintentionally stepped on his goalkeeper's foot.
And because Martin Atkinson didn't blow his whistle before Smith Rowe's shot rippled the back of the net, VAR declared that the goal had to be given.
Crazy, we know...
Before the half-time interval, Bruno Fernandes levelled the scores with a well-taken goal, Fred redeeming himself by grabbing the assist. That wasn't the end of the talking points from the opening period of play, though.
Just prior to the teams leaving the pitch for a 15-minute break, Arsenal should have been awarded a penalty.
United captain Harry Maguire clearly pulled Takehiro Tomiyasu by the arm in the box, however, the referee didn't spot the infraction.
Amazingly, VAR didn't step in and overturn the decision either.
Video: Maguire pulls down Tomiyasu in the box
How was that not given?!
Maguire only had eyes for the man and he blatantly pulled him to the floor and prevented him from making contact with the ball.
United were unfortunate in the way Arsenal's opener came about, but they were hugely lucky at the end of the first half.