"Messi was decisive when he was on the pitch. He's used to deciding matches and he did so again," Simeone told AS.
"I think Barcelona dominated every area of the game, whether defending or in possession. We didn't play a good game.
"We started the second half well, but the quick equaliser put us off our stride again. Our idea was to try and pressure higher up the pitch, but Barcelona absolutely dominated the game."
Consequence of the victory, the Catalans extended their 100% start after three Liga games, while the Rojiblancos - who had also won their opening two outings - suffer a first defeat.