Isak, second in the Premier League's top scorers' race with six goals, was substituted in the 66th minute with the score at 1-1 away to Fenerbahçe.
Just three minutes later, he headed in to make it 2-1. But Isak was not the hero of the match for Liverpool.
Fenerbahçe equalised to make it 2-2 just four minutes later. Another six minutes after that, the Turkish giants completed the comeback when Vedat Muriqi headed in to make it 3-2, sending the vast majority of the stadium into raptures.
It was the winning goal, meaning Liverpool have now suffered their first defeat of the Champions League league phase after starting with three straight victories.
Real Madrid's perfect start to the Champions League continues, however. But it was far from straightforward against AEK in Athens. The home team led 1-0 and then 2-1, but Real Madrid came back to win 3-2. The comeback featured, among other things, a backheel goal by Jude Bellingham to make it 1-1 and a rocket from Federico Valverde to make it 3-2 in extra time.
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