Two goals apiece from Preston Fearon and Callum Marshall, either side of an own goal, secured the win for the young Hammers, while Aaron Collins won and scored a penalty for the hosts.
Here are our ratings after the Vertu Trophy defeat.
1. How we rated the MK Dons players after the defeat to West Ham U21s
It was a night to forget for almost everyone on the pitch at Stadium MK | Jane Russell
2. Connal Trueman - 4.5
Made two big stops but can't have been pleased with any of the goals he conceded | Jane Russell
3. Callum Tripp - 4
A pretty forgettable night. West Ham had a lot of joy down his flank especially in the first-half, and his mistake led to the third | Jane Russell
4. Kobe Sinclair-Linton - 4.5
Showed a little promise but too many heavy touches too often let West Ham in | Jane Russell
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