Bruno Fernandes scored both goals, a customarily cool penalty early on and delightful second-half shot, to secure three points in the competition, at a sweltering MetLife Stadium.
Jarrod Bowen pulled one back for the Hammers, with a clinical finish, and was only denied an equaliser by a smart save from Altay Bayindir in the dying seconds.
Yet Ruben Amorim's side, who left Bryan Mbeumo out of the squad as he builds up his fitness, were good value for the victory after an impressive team performance.
FIRST HALF - ENERGETIC REDS ON TOP
United made a blistering start, coming out of the blocks, almost scoring in the opening minute.