The 19-year-old found the net after seven minutes after a pinpoint pass from Herrera.
It was the icing on the cake after a display full of attacking promise in the absence of top scorer Zlatan Ibrahimovic.
And the teenager took to Instagram to express his happiness at the result.
“Massive win and delighted to score another goal,” he said.
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Which Manchester United players impressed during their win over Chelsea?
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Herrera was also happy to get on the scoresheet.
The Spain international doubled United’s lead just four minutes after half-time.
“Perfect day at old Trafford,” he posted on Instagram.
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David De Gea had precious little to do as United successfully nullified Chelsea.
The Spain international was restored to the side after missing their 1-1 draw with Anderlecht on Thursday.
And the goalkeeper posted a picture of him looking chuffed with the result.
“I love to win at Old Trafford,” he said on Instagram.