Lukaku made the perfect start to his Manchester United career with two goals at Old Trafford against the Hammers.
The brace took his record to 11 in 13 games against the east Londoners.
But the emphatic result puts United at the top of the table after the first weekend and Lukaku was delighted to take all three points.
He said: "To play in front of such a crowd is a dream come true but most importantly is the three points.
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Romelu Lukaku applauds Manchester United fans
"When you play for Manchester United, you have a job to do and mine is to score goals. It is promising.
"The manager wants me to be a leader for the team and create as much as I can. We work hard in training and it is paying off.
"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."