Pep Guardiola gave his happy Manchester City players a stark reminder that Paris St Germain will be even more dangerous in the second leg.
The Blues will take a 2-1 first-leg lead back to the Etihad Stadium next Tuesday, through goals from Kevin De Bruyne and Riyad Mahrez, making them firm favourites to progress to the final in Istanbul next month.
But the way PSG played in the first half, and the way City struggled to impose themselves in that 45 minutes, serves as a lesson for the second leg.
Said Guardiola: "In the 45 minutes we played to not lose the ball but without any intention to be aggressive or break the lines with the passes, play quicker to the wingers or behind the lines.
"We couldn't do it and in the second half was much much better. That's the reason why - our football was better.
"The way we were more aggressive with and without the ball with intention, being patient all the time but when Riyad (Mahrez) arrived with a sense of danger in those positions, Phil (Foden) was more involved in the game, it was much better."
But Guardiola was quick to dredge up the fact that PSG reached the semi-final by scoring three at Bayern Munich and four at Barcelona.
He could also have pointed out that in the group stages, they lost 2-1 at home to Manchester United before a 3-1 victory at Old Trafford saw them qualify and dump the Reds into the Europa League.
The City celebrations at the end were muted, and Guardiola quickly reinforced the point that the difficulties City faced in the first half will be encountered again in the home leg.
"I understand the players, I know it is not easy," said Guardiola. "We faced a team that scored four goals at Camp Nou, that scored three goals in Munich.
"It is a team that is able to do whatever they want because they have the quality to do it. That's why when you start the game you are a little bit cautious."
