Diego Simeone had the last laugh. After resting his key players for the La Liga meeting three days earlier, Atletico Madrid arrived at Camp Nou with a full squad, a clear game plan, and the quality to execute it. They leave with a 2-0 advantage and a place in the semi-finals firmly within their grasp.
Barcelona controlled the first half and created the better chances. Marcus Rashford, operating as the primary attacking outlet with Raphinha still absent, tested Juan Musso repeatedly in the opening stages but could not convert. Atletico stayed disciplined, waited, and then got the moment they needed.
The 44th minute was the turning point. Pau Cubarsi, chasing Giuliano Simeone as he ran clear through on goal, brought him down from behind. The referee showed yellow. VAR intervened and upgraded it to red. From the resulting free kick, Julian Alvarez bent a stunning effort into the top corner from 25 yards. It was his ninth Champions League goal of the season. Barcelona went into half-time a goal down and a man short.
Hansi Flick responded at the break, withdrawing Lewandowski and the booked Pedri and sending on Gavi and Fermin Lopez to give his side legs. Barca showed enormous character in the second half. They kept pushing, kept creating. But with 20 minutes left, Atletico struck on the counter. Alexander Sorloth, on as a substitute, turned home a cross from Matteo Ruggeri to make it two.
Flick was furious in his post-match press conference, and not primarily about the red card. In the 54th minute, with Atletico already ahead, goalkeeper Juan Musso played a short goal-kick to Marc Pubill, who stopped the ball with his hand and returned it to his keeper. The referee waved away Barcelona's protests. VAR did not intervene. Pubill was already on a booking. Flick said after the match: "It should be a penalty and a second yellow for the player. What is the point of having VAR?" Barcelona have since filed a formal complaint with UEFA, describing the officiating as incomprehensible and requesting access to referee communications.
The result ends Barcelona's 14-game unbeaten run at the renovated Spotify Camp Nou. Atletico have not won here since 2006. The second leg is at the Riyadh Air Metropolitano on Tuesday, April 14. Barca need to win by two goals minimum to advance. Flick's message after the final whistle was brief: "We will fight. It is not done yet."