The hosts, quarter-finalists in this competition only two years ago, came close to breaking the deadlock early on when Vangelis Pavlidis had a towering header from inside the six-yard box tipped over the bar by Jan Oblak.
Fredrik Aursnes then saw his effort from distance saved, before the Norwegian turned provider as the Eagles finally went 1-0 up, playing a defence-splitting pass to an unmarked Kerem Akturkoglu, who tucked into the bottom corner.
That was only the sixth goal Diego Simeone’s side had conceded in ten outings this season, and it seemed to wake them up.
Samuel Lino soon had a couple of chances, spraying wide of the far post and heading off target from a good position. That lack of cutting nearly came back to bite them, as with the half-time whistle approaching, Pavlidis nearly doubled his side’s lead with an off-balance shot that brushed the far post.
The Eagles did not have to wait long for their second goal though, as VAR intervened to controversially award a penalty for a foul on Pavlidis shortly after the break.
Angel Di Maria duly sent Oblak the wrong way with his spot kick to make it 2-0, and the Argentine had another chance minutes later, surging through one-on-one and seeing his shot saved.
That killed off a subdued Atleti, who offered nothing going forward. They had still not registered a shot on target by the time Benfica made it 3-0, as Alexander Bah brushed off his man and nodded home Jan-Niklas Beste’s corner at the back post.
It had turned into a mauling by now, and there was still worse to come for the visitors, who have now won only one of their last ten Champions League away games.
The hosts, who have won nine successive fixtures across all competitions at Estadio da Luz, completed the rout when Zeki Amdouni was tripped in the area by Reinaldo, allowing Orkun Kokcu to emphatically smash home the fourth from the spot.