Manchester United recorded their biggest Old Trafford win over Chelsea since 1965 to condemn Frank Lampard to a miserable start as a Premier League manager.
Marcus Rashford scored twice, either side of a close-range effort from Anthony Martial, who had been given the number nine shirt back following the sale of Romelu Lukaku to Inter Milan.
Substitute Daniel James completed the scoring with a goal on his debut nine minutes from time.
The final scoreline was harsh on the visitors, who were the better side before the break and hit the frame of the goal through Tammy Abraham and Emerson, but still suffered their worst ever opening-day defeat in 104 league seasons.
The ecstatic home supporters did not care about that though, as the negativity of a difficult summer was swept away by their best result against Chelsea since they beat them by the same score in the 1994 FA Cup final.