The Argentine striker scored for the second successive match as Atletico moved within two points of LaLiga leaders Barca, then addressed the comments that had soured his relationship with fans at the Metropolitano.
"I'd like to apologise to our fans for what I said at the World Cup; it was a mistake in terms of how I said it and the timing," Alvarez told Spanish broadcaster Movistar Plus.
"I understand why the fans are angry. If I were a fan, I'd be angry too. Especially given how they've supported me since I arrived."
Alvarez said during the 2026 World Cup that he "wanted to fulfil his dream" of playing for Barcelona, triggering a transfer dispute that stretched through pre-season and the summer window as Atletico refused to sell to their rivals.
Regularly booed at home this season, Alvarez received a standing ovation from some supporters after Saturday's goal.
"I hope that with hard work and humility I can turn this situation around," he said.
"I've been feeling better in recent matches - both physically and on the ball. I want to help the team and give my best."
Second-placed Atletico have 25 points. Real Madrid, third with 21, visit Barcelona at Camp Nou on Sunday for the season's first Clasico.
LaLiga
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