Ruben Amorim said Sporting’s 4-1 rout of Manchester City was a dream way to sign off in his last home game as head coach but warned that when taking over Manchester United ­he cannot be as “defensive” as the ^­Portuguese champions.

After Phil Foden opened the scoring, Viktor Gyökeres’s hat-trick and a Maximiliano Araújo strike handed City a first Champions League loss of the season. Yet Amorim was clear the result will mean nothing when he starts at United next week.

Related: Rúben Amorim’s Sporting hammer Manchester City with Gyökeres treble

“We cannot transport one reality to another,” he said. “United cannot play the way we play, they cannot be so defensive. Of course it’s good to beat City. But I’ll be living in a different world, we’ll have to start from a different point.”

He was asked if this was a dream manner to sign off. “Yes. I couldn’t ask for anything better, it was a very important moment for all. But we had the luck – this was a one off.”

Before the game Amorim quipped that some United fans would view him as the “new Ferguson” if Sporting beat their great rivals. “I was playing with words when I said that I am not going to read anything for six months,” said Amorim. “I am going to focus on the team.”

At the end the 39-year-old was given a rapturous reception from the home supporters and the bumps from his players. “I thanked everyone for the win,” he said. “If we hadn’t won the match, the moment wouldn’t be so nice. It was better with a win over City.”

“I wasn’t expecting to be raised in the air, I know what I did for them, and what they did for me. I will keep these memories with me for ever. The most important moment for me was when we lost 5-0 to City [two years ago] and everyone applauded.”

Pep Guardiola struck a defiant note. “It’s a difficult moment, but I’m here and want to fight, I like these moments. I don’t want to give up,” City’s manager said. “You cannot say much when you lose 4-1. Emotionally we were not stable enough. Emotionally we have to be more stable.

“It is what it is. Now it is difficult, but I want to fight and not give up. There is a challenge ahead of me.”