Romelu Lukaku responded to José Mourinho’s demand he should be a Manchester United “leader” by scoring twice on his Premier League debut as West Ham United were beaten 4-0 at Old Trafford on Sunday.

Lukaku broke the deadlock on 33 minutes before doubling United’s advantage eight minutes into the second half. Further goals from Anthony Martial and Paul Pogba on 87 and 90 minutes put Mourinho’s team top of the Premier League on goal difference.

Afterwards Lukaku, the club’s £75m summer signing, revealed he is revelling in the responsibility Mourinho has placed on his shoulders. “The manager wants me to be a leader for the team and create as much as I can,” the 24-year-old said. “We work hard in training and it is paying off. When you play for Manchester United you have a job to do and mine is to score goals. It is promising. The fans want to see attractive football and we have to stick to that. They will be pleased today. It is just the start. We need to keep working to the manager’s plan.”

Of Lukaku’s instant impact, Mourinho said: “He scored in the Super Cup [defeat by Real Madrid], he scored today. He is playing well, he is working hard. He likes the team and the team likes him. For every striker, he can play phenomenally well but, if he doesn’t score goals, he is not happy. [But] strikers can play very well for the team and no pressure from me.”

Play Video 0:43 Lukaku double pleases Mourinho as Manchester United win – video

The Portuguese said United’s display and confidence was more important than being top of the table after the opening weekend of the Premier League season. He said: “The fact we start winning and are top, it means nothing. The performance and the levels of confidence is what means a lot to me. We lost two points against them last season [in a 1-1 draw] and had similar games where we dominated. Today we got the three points. The reality is that in the last part of the game, instead of being boring and controlling the game, we scored a third goal and we could enjoy it. What pleased the most was the win. Because many times last season we deserved to win and didn’t so the fact we won the match was the most important thing. We made mistakes and have room for improvement but it was a solid performance.”

Romelu Lukaku gives Manchester United dream start against West Ham Read more

In addition to Lukaku, Nemanja Matic caught the eye against an outclassed West Ham with a display which offered United control over the midfield battle. Mourinho brought him in from Chelsea for £40m and was asked why the champions had allowed the sale.

“It depends on what is happening or what was happening behind doors and we don’t know,” he said. “I never thought it was possible unless something special was happening and his agent told me something special was happening. We have him and we are very happy. He was a player this team needs.”

Mourinho suggested Victor Lindelof, a central defender who cost £31m in the close season, needs time to adjust. The Swede did not make the match-day squad, and the manager said: “Real Madrid [in the Super Cup] was too early for him. He played because [Phil] Jones and [Eric] Bailly were both suspended. I had players coming from different leagues to the Premier League and normally it is not easy.

“Lukaku and Matic have years of experience of the Premier League. Ricardo Carvalho was one of the best defenders in the history of the Premier League but in the beginning he struggled. Victor needs time and he will get time.”

Slaven Bilic, the West Ham manager, admitted: “They were better with the ball and better without the ball.”