Manchester United are still reeling after their 2-1 derby loss to rivals Manchester City on Sunday.
Nicolas Otamendi got the winner, making the most of Romelu Lukaku's awful clearance, after Marcus Rashford had cancelled out David Silva's opener.
City's victory moves them 11 points clear at the top of the table after just 16 games, and while Premier League title number three is not yet secured, it is certainly in their hands.
However, the game will unfortunately be remembered for the ugly scenes in the Old Trafford tunnel after the final whistle, as United boss Jose Mourinho had water, milk and bottles thrown at him.
City coach Mikel Arteta suffered a cut eyebrow after he was struck by a bottle, with the home side's frustration boiling over as their rivals loudly celebrated the win.
One big talking point to come out of the game, though, was Ander Herrera's booking for simulation.
The former Atheltic Bilbao midfielder appeared to initiate contact with Otamendi in the penalty area, and referee Michael Oliver had no hesitation in showing Herrera a yellow card.
City's players reacted furiously to the Spaniard, though both the player and Mourinho were furious that a spot kick wasn't awarded, which would've given United the chance to level the game.
Speaking to Sky Sports after the match, Mourinho said he felt 'sorry' for the official, who had failed to give the appropriate decision.
"My first reaction is I feel sorry for referee Michael Oliver because he had a very good match, but unfortunately he made an important mistake," he started.
"The result was made with a big penalty not given [on Ander Herrera]. That would have been 2-2 with 20 minutes to go.
"The referee made a mistake which can happen."
And Herrera remains equally annoyed, claiming that Oliver's decision was 'amazing'.
He also added that the official was inconsistent, as he believes two City players should've suffered the same fate for diving in the first-half.
"I think the penalty [decision] is amazing," he admitted. "He didn't expect to arrive for the ball. I touched the ball first and he stamped on my foot. I think everyone saw it.
"Everyone can make mistakes too, also the referee. I didn't deserve the yellow card. In the first half, there were similar situations with Gabriel Jesus and Leroy Sane, and they didn't
get yellow cards.
"That is my fourth yellow card and that is a big problem for me."
Herrera consequently wants to see bookings retrospectively chalked off if they are given for a wrong decision, something he says has been successful in his homeland.
Players in La Liga can appeal those decisions, which ultimately can prevent possible suspensions, something Herrera will have to face up to if he receives another yellow card.
"In Spain, if you get something undeserved you can appeal and they take it out," he stated.
"That is one of the things that could improve the Premier League because it is an amazing thing, an amazing competition.
"But it is a real shame that if you don't deserve a yellow card, you cannot appeal afterwards. Hopefully, one day, that rule can change."
Unfortunately for the midfielder, his thoughts will ultimately fall on deaf ears, as all the evidence suggests Oliver made the right call.
Herrera and United will look to pick themselves up with a victory at home to Bournemouth tomorrow night.