Ernesto Valverde was full of praise for Barcelona as they overcame Olympiakos 3-1 in a testing encounter at the Nou Camp on Wednesday.
Dimitrios Nikolaou was unfortunate to turn the ball into his own net for the opening goal on 18 minutes while Gerard Pique made life difficult for Barca when he was dismissed on 42 minutes for a second yellow card.
Lionel Messi though resumed normal service when he netted his 100th European goal on 61 minutes before Lucas Digne put the result beyond doubt with 64 minutes played.
Nikolaou went some way to make up for his early error with a goal for the Greek champions in the last minute of the tie.
The result left Barca on top of Group D with nine points, ahead of Juventus (6), Sporting (3) and Olympiakos, who are yet to register a point.
After the game, Valverde said: "The match showed us there are no easy games. We should recognise how important this victory is, we secured three difficult points.”
Valverde further explained how the red card affected Barca's performance.
"We knew they'd get stronger once we went down to 10 men. That's why we needed to find a second goal, so things would become easier.
"They came to defend and find a goal on the counter-attack. With our opponents playing so deep, it was tough to find rhythm and they played a game that suited them.
"But he (Messi) splits the game up and looks for players to link up with. When he's heading towards goal, he always looks for team-mates to finish off his moves."