Manuel Pellegrini admitted he was “very worried” at half-time and would have changed his entire team had he been able to after Manchester City dug themselves out of hole to reach the fifth round of the FA Cup at Watford’s expense.

The City boss believed his side lacked intensity in the first half as goals from Fernando Forestieri and Troy Deeney gave the Hornets a 2-0 lead at the break. But the Premier League side upped their game after the break and Sergio Aguero’s hat-trick and a mistake from Jonathan Bond which allowed Aleksandar Kolarov saw the quadruple chasers through to the next round.

Asked how concerned it was the interval, Pellegrini replied: “Yes of course, very worried because he talked to the players before the match about this cup, the Spanish Cup, the Italian Cup, everywhere the team playing in a lower division has a lot of motivation and if you don’t play with 100 per cent concentration or intensity, you’re not going to win the game. I think that Watford did in the first 45 minutes and we played jogging [pace] and in that way it’s impossible to win.”

“I didn’t think we were going to have an easy game but the important thing is the players must not believe we have an easy game because the play a team from the Championship,” the City boss responded when asked if his team had taken the Hornets lightly. “But they had a very good reaction for the second half, they changed absolutely everything to what we needed. We played with a higher tempo, with a higher pace and we continued playing the way we have the whole season at the Etihad.”

Pellegrini conceded that if Watford had managed to get a third goal, he believed the tie would have been over, explaining: “If I could change 11 players at half-time I would have changed all of them. The whole team didn’t do the things that we normally do so the most important thing for me is that Watford didn’t score the third goal. If they scored the third goal the game was finished.

“So I think it was very important for us to make people defend – we defended very badly in the first half – second, to have the midfield with some intensity, try to recover the ball and especially to make the movements the forwards must do if you want to create the space in a defence that had eight or nine players behind the ball. But I think we took charge in the second half.”