The Reds threw away a two-goal lead but scored the winning goal after Antoine Griezmann had been sent off.
The in-form Mohamed Salah put Liverpool ahead at Estadio Wanda Metropolitano with just eight minutes played. The Egyptian was forced wide by the loose ball but dribbled his way inside, beating several Atleti defenders in the process, before firing in a shot that took a deflection off Geoffrey Kondogbia and nestled into the net.
Naby Keita extended the Reds’ lead in the 14th minute with a volley from outside the box.
Twenty minutes in, Barcelona loanee Antoine Griezmann pulled a goal back for the home side. The Frenchman got the slightest of touches to his colleague Koke’s shot, which took it past Alisson.
Los Rojiblancos were level in the 34th minute through Griezmann’s second of the night; the forward collected the ball from Joao Felix, took it away from Virgil Van Dijk with his first touch, and scored with his second.
Griezmann turned from hero to zero seven minutes into the second half when he caught Roberto Firmino in the face with a high boot. The referee did not hesitate in showing him the red card, bringing the home side down to ten men.
Jurgen Klopp’s men capitalized on the numbers advantage by piling on the pressure that eventually resulted in a penalty being awarded to them. Salah stepped up to score from the spot, sealing all three points for the Reds.
In the other Group B game, Porto condemned AC Milan to their third straight defeat on their return to the Champions League. The Portuguese outfit dominated proceedings throughout the match and was rewarded for their control when livewire Luis Diaz found the net in the 65th minute.
The Colombian was a constant menace to the Milanese defense and had hit the post earlier in the game. His fierce strike for the goal was more accurate, as it skimmed past Ciprian Taturusanu and into the back of the net.
Ravaged by injuries and sickness, have a mountain of a task ahead of them. Stefano Pioli’s side is four points behind Porto and Atletico, and nine behind Liverpool, with three matches still to play.