Summer signing Hojlund rifled United ahead with his fourth Premier League goal in as many games, with 19-year-old Garnacho then seeing an effort deflect in off Nayef Aguerd before firing home United’s third against David Moyes’ Hammers.
The goalscorers and Thursday’s matchwinner Mainoo mimicked West Ham forward Mohammed Kudus’ celebration after Garnacho’s first goal, sitting together on the advertising hoardings.
It provided a fantastic image of three young talents that offer hope for a bright future at United, whose season has been bumpy for the most part but is starting to show signs of improvement.
The only negative for Erik Ten Hag’s side was the injury that saw a grimacing Lisandro Martinez replaced with 20 minutes remaining.
Sunday’s match was the closest home fixture to the 66th anniversary of the Munich air disaster on February 6.
Ten Hag and Moyes, United managers present and past, carried wreaths on to the field before kick-off as all inside Old Trafford remembered the 23 people, including eight players, who died in 1958.
The opening goal arrived in the 23rd minute through what is becoming a reliable source for United.
Casemiro battled to win the ball high up the field and it fell to Hojlund, who superbly cut away from Aguerd and unleashed an 18-yard piledriver low past Areola.
— Manchester United (@ManUtd) February 4, 2024
Ben Johnson saw an audacious long-range effort sting Onana’s palms as West Ham attempted to level.
Kurt Zouma went down in the box after being caught in the face by Hojlund and Kudus saw a header saved as the visitors ended the opening period with 14 scoreless attempts.
It was a missed chance that was punished immediately.
United attacked in numbers and Fernandes’ cross-field ball to Garnacho was followed by the winger cutting on to his left and hitting a drive that went in off Aguerd in the 49th minute.
The grinning teenager copied Kudus’ celebration by sitting on the advertising boards, with Hojlund and Mainoo joining him.
West Ham were only threatening in fits and starts. Emerson wasted another opportunity by spooning an effort at Onana, with Dalot storming back to block a fizzing Jarrod Bowen strike. Old Trafford roared in appreciation.
But emotions quickly turned to concern as Martinez pulled up.
Only recently back from a foot injury, he clutched his right knee after Vladimir Coufal landed on him awkwardly. Martinez was able to continue, only to fall to the deck again and be replaced after Dalot’s brilliant block.
West Ham tried to pull one back and Zouma hooked wide, before substitute Kalvin Phillips’ dreadful effort got the kind of reception you would expect for a Manchester City loanee and former Leeds star.
United were thanking him in the 84th minute. Pressure from Scott McTominay and Hojlund resulted in Phillips coughing up possession, starting a counter-attack that ended with Garnacho firing home in the 84th minute.
“We want Glazers out” echoed around Old Trafford in stoppage time, when McTominay went close to a fourth.