The implementation of VAR has been one of the most controversial new rules in the Premier League's history, as Liverpool found out on Saturday at Villa Park.
The Reds were trailing 1-0 to Aston Villa after Trezeguet's strike was awarded, then checked for VAR for offside, before being allowed to stand.
Six minutes later, Liverpool thought they had equalised: Sadio Mane's cross found Roberto Firmino at the far post and the Brazilian slotted home.
The flag was raised by the assistant referee but because referee Jonathan Moss hadn't blown his whistle, the goal could still be awarded via VAR if no wrongdoing was found.
But incredibly, after the detailed calculations were concluded, it was confirmed that the 28-year-old's armpit was found to be offside, according to the Premier League.
A tweet from the league's official feed read: "Liverpool's Roberto Firmino was flagged offside before putting the ball in the net against Aston Villa and the decision was confirmed by VAR.
"The red line signifies Firmino and was aligned to his armpit, which was marginally ahead of the last Villa defender."
The Reds went into the game with nine wins from 10 games and a six-point lead at the top, but after the tighest of margins could find themselves in danger of losing their record.
