Substitute Marcus Rashford scored an injury-time winner as Manchester United finally overhauled a stubborn Hull at a sodden KCOM Stadium.
The 18-year-old – making his first appearance of the season – steered home Wayne Rooney’s cross to spark wild celebrations on the away bench.
Moments earlier, David Meyler had blazed over in a rare Hull attack.
But it was a deserved win for United, who had gone close though Rooney, Zlatan Ibrahimovic and Paul Pogba.
United and Chelsea are now the only Premier League sides with a 100% record from three games, with Manchester City – who have two wins from two games – playing West Ham on Sunday.
Rashford’s winner was the climax to a performance of persistence and intelligence from the visitors, who changed tack several times before eventually breaking down Hull.
Ibrahimovic arrived at Old Trafford with a reputation for audacity, but, in the first half, it was his physical size rather than mercurial skill that posed most threat.
Offering himself as a constant target in the box, the Swede headed just over the bar in the 10th minute before an extravagant backheel found the side-netting.
The excellent Curtis Davies blocked the more direct route to goal after the break, but the guile of Henrikh Mkhitaryan and the pace of fellow substitute Rashford stretched the Hull defence in different directions and, finally, beyond breaking point.
A back muscle injury which is likely to rule Marouane Fellaini out for several weeks means United will need to show similar adaptability when they meet Manchester City in their next match
Tigers fall just short
With Harry Maguire returning from injury on the bench, former Manchester United assistant manager Mike Phelan had a season-high 14 fit senior professionals available for Hull.
But what his squad lacks in numbers, it makes up for in spirit.
Alongside Davies, Sam Clucas impressed in midfield, while Adama Diomande and Abel Hernandez chased hard to make something from the few scraps in attack.
Before Meyler’s late wasted chance, Tom Huddlestone saw a shot deflect just wide with David De Gea hopelessly wrong-footed as they briefly threatened a smash-and-grab victory.
But, after wins over Leicester and Swansea in their opening two games, their 100% start to their top-flight campaign is over.
The uncertainty over the club’s future might also be at an end, however, with vice-chairman Ehab Allam writing in the programme that the match could be his family’s last as owners, with takeover talks with a Chinese consortium well advanced.
That deal may free up funds to supplement the Tigers’ threadbare squad – Tottenham’s Ryan Mason is a target – and help them continue to defy the Premier League’s usual rules of gravity.
MOTD analysis on Rashford
Alan Shearer: “I don’t think it will be long before he is a regular. It has to be absolutely brilliant for him at that football club, working, training and socialising with Zlatan Ibrahimovic and Wayne Rooney.”
Ruud Gullit: “What I like about Rashford is that he goes straight past players. He gives you opportunities. I hope Manchester United manager Jose Mourinho considers him more because he’s a great player.”