Juan Mata and Zlatan Ibrahimovic fired Manchester United to a sixth straight victory at 10-man West Ham.
United were labouring against a Hammers side holding firm despite being a man down from the 15th minute after the controversial dismissal of Sofiane Feghouli.
But Jose Mourinho sent on Mata and Marcus Rashford at the start of the second half and the substitutes combined to break the deadlock. Ibrahimovic, who hit 50 goals in 2016, then opened his account for the new year as United ran out 2-0 winners.
However, the defeat was harsh on West Ham, who were up against it from the moment referee Mike Dean brandished his fifth red card in 15 matches this season.