Manuel Lanzini’s ninth-minute effort, his first goal in almost 12 months and only his second since May 2019, proved enough to take David Moyes’ men into the last 16.
Lanzini’s goal was just reward for West Ham’s flying start.
Ryan Fredericks eased between Jadon Sancho and Alex Telles before cutting,
a low cross back to the Argentine, who finished into the bottom corner.
Three times in the final five minutes the visitors should have wrapped up victory.
But, Andriy Yarmolenko, Mark Noble and Jarrod Bowen all failed to hit the target,
In the end though, it didn’t matter.
It was the first Old Trafford triumph for the Hammers since Carlos Tevez’s matchwinner,
in 2007 kept them in the Premier League – and their first in a cup competition since Paolo di Canio scored the only goal in an FA Cup meeting in 2001.
For Manchester United and Solskjaer it is an early end to their hopes of securing the first available silverware of the season.
And ending the wait for a trophy that stretches back to 2017.