The record-breaking Anfield crowd witnessed a frantic start to proceedings in the second consecutive UCL opener between these sides, with Alexander Isak dragging wide seconds after kick-off.
An open and entertaining quarter of an hour followed before Atleti stunned the home fans, going ahead when Julian Alvarez threaded the ball through to Marcos Llorente, who lifted a side-foot finish over Alisson Becker for a remarkable fifth Anfield UCL goal of his career.
Liverpool’s high defensive line was being exploited, and were it not for a strong palm from Alisson, Alvarez would have doubled Atletico’s advantage after a sharp breakaway.
Despite some concerning defensive lapses, the Reds weren’t without attacking threat, as Florian Wirtz tested Jan Oblak with a close-range half-volley, albeit during an offside play.
Yet that should have served as a warning sign for the visitors, who soon found themselves pegged back. Bradley Barcola's low shot was well saved by Oblak, but the danger hadn’t passed, and Atleti were unable to prevent Ronald Araujo from neatly flicking the ball into the path of Dominik Szoboszlai, who delicately stroked home the leveller ahead of the half-time break.
Having failed to keep a clean sheet for the 17th time in their last 18 UCL matches, Los Rojiblancos had work to do if they were to come away with all three points.
Yet any aspirations of a first-ever win over an English side in the UCL group/league phase were dealt a significant blow shortly after the restart.
Barcola should have been the man to do it when he found himself one-on-one with Oblak, only to sweep wide of the target with the goal at his mercy, but in the next play, the ball fell kindly for Alexis Mac Allister to rifle home from the edge of the box.
The intensity of the first half had naturally petered out as the contest wore on, and with Liverpool now ahead, they were able to establish control of the match.
Los Colchoneros pushed for a late equaliser, but the Reds stood firm, and despite a late disallowed goal from substitute Jeremie Frimpong, did enough to get over the line.
Diego Simeone’s 14th successive UCL campaign as Atleti manager isn’t off to the best start, and after last season’s 3-2 Anfield defeat, it marks the first time the Madrid side have lost successive UCL openers this century (W7, D5, L4).
In the opposite dugout, Iraola will be much more content, overseeing Liverpool’s 18th Anfield win from their last 19 in European group/league phase games (L1).
Flashscore Man of the Match: Dominik Szoboszlai (Liverpool)