Tensions boiled over in the second half of Atletico Madrid's game against Porto, with two players sent off and all-in brawl involving both sets of players and several members of the respective coaching staffs.
After the first 45 minutes passed without incident, the game burst into life as Antoine Griezmann put Atletico ahead early in the second half.
Barely 10 minutes later, the visitors found themselves down to 10 men as Yannick Carrasco was sent off for lashing out at Porto midfielder Otavio, who had attempted to take a quick free-kick.
Carrasco first held onto the ball to prevent Porto from restarting the game, before taking a swipe at Otavio who had reached for the ball.
As pushing and shoving ensued, the Belgian was knocked to the ground himself but that was not enough to dissuade referee Clement Turpin from sending him off.
Otavio was booked for his role in the melee, as were Atleti midfielder Angel Correa and Porto's captain Pepe.
Never one to shy away from controversy, the veteran defender, a former Real Madrid player, had to be held back as he shouted threateningly towards Atleti's defender Mario Hermoso.
Three minutes after Carrasco's sending off, an even bigger brawl unfolded after Porto defender Wendell was sent off barely five minutes after coming on.
The Brazilian defender reached for the ball as he tried to take a quick throw in in front of the Atleti bench, but appeared to strike Matheus Cunha with his elbow as the latter raced in to try and take the ball away.
Cunha went down right in front of his team's dugout, sparking a full-on brawl as Porto players felt the forward had made the most of it.
Turpin showed Wendell a straight red, but the Porto defender bizarrely remained on the pitch for a few minutes, as the French referee looked to restore some calm before eventually ordering Wendell off the pitch.
Correa and Rodrigo De Paul scored late goals for Atleti, as the reigning LaLiga champions finished second behind Liverpool to qualify for the knockout stages.