I dont understand why going 3 at the back was a bad decision? Bringing on your best defender who can also add some height is perfectly sensible. Not only defensively, but in allowing your full backs to push up and provide width which we are lacking from Coutinho and Mane being absent, it can help in an attacking sense too. Those same full backs can also help the midfield provide more control of the game. As others have said, had Klavan not made a basic error, it would have been viewed as a good change.