Paul Pogba had gone five games without scoring following his £89 million ($115 million, 102 million euros) arrival from Juventus and had to endure criticism of some below-par performances.
But the 23-year-old France midfielder was on the scoresheet at last in the 42nd minute at Old Trafford.
Timing his run perfectly, Pogba met Daley Blind’s corner with a powerful header that gave Leicester goalkeeper Ron-Robert Zieler no chance.
It was United’s fourth goal of the half as Jose Mourinho’s side demolished the Premier League champions.
POGBA: ‘I’m v happy for the result and for the goal. I never look at newspapers but I always say one thing: at the end we will see”
Paul Pogba continued his impressive premier league carrier as he once again adjudged man of match.
The remaining united goal scorers were Smalling, Mata and Rashford. Leicester City’s second-half substitute Gray reduced the deficit to 3.