It is successive Premier League victories for United as they continue their unbeaten start to 2024.
Prior to kick-off, managers Erik ten Hag and David Moyes carried out wreaths to honour the victims of the Munich air disaster, which happened 66 years ago.
The first chance of the match fell to West Ham on 11 minutes, when Tomas Soucek’s deflected header from James Ward-Prowse’s outswinging corner forced a fine save from Andre Onana.
At the other end, Bruno Fernandes’ dipping long-range strike was pushed away at full stretch by Alphonse Areola.
Man Utd took the lead on 23 minutes through Hojlund, who unleashed a brilliant low right-footed shot past Areola to score in his fourth consecutive Premier League appearance.
Hojlund is only the second player to find the back of the net on his 21st birthday in the competition, along with Noel Whelan in 1995.
West Ham made a change during the break with Lukasz Fabianski replacing Areola due to an apparent head injury.
The Hammers had a great chance to equalise on 48 minutes as Emerson dispossessed Harry Maguire and ran through on goal, but the Italian fired his shot over the crossbar.
Less than a minute later, Man Utd doubled their lead when Garnacho cut inside before his left-footed attempt went in via a deflection off Nayef Aguerd. Garnacho celebrated by sitting on the advertising hoardings, a celebration used often this season by West Ham’s Mohammed Kudus.
West Ham did have a chance to reduce the deficit and Jarrod Bowen should have made more of a 1v1 situation, but his attempt was thwarted by Diogo Dalot, who slid in to produce a brilliant last-ditch tackle.
United were dealt a blow on 70 minutes when Lisandro Martinez was forced off with an injury.
Garnacho scored his second of the match with six minutes remaining. Scott McTominay took the ball off West Ham substitute Kalvin Phillips and surged forward before playing in the Argentinian to slot home.
McTominay could have added a fourth, but dragged his shot wide in stoppage time.
United move above West Ham and have 38 points, eight behind fourth-placed Aston Villa.
The Hammers are two points below in seventh.
Source : premierleague