Match ends, Bournemouth 1, Manchester United 0.
Manchester United manager Ole Gunnar Solskjaer said it was a "step back for us" as his side's three-match winning run ended at Bournemouth.
United made a positive start after going four unbeaten but their new-found belief seemed to evaporate in driving rain and swirling wind on the south coast.
Former United trainee Joshua King struck on the stroke of half-time to claim Bournemouth's first goal in nearly six hours and give the Cherries their first win since September.
United came into the game in seventh place but now have a haul of 13 points from 11 games - their lowest at this stage of a league campaign since 1986-87 (11).
"If you want to get into the top four you need to win games like this," said Solskjaer. "It is a step back for us today, but we need to shake it off and go again."
King, who scored the winner in Bournemouth's only previous Premier League win against the Red Devils in 2015, was allowed to chest down Adam Smith's cross into the box before turning Aaron Wan-Bissaka and volleying between David de Gea's legs from close range.
The Cherries carried that momentum into the second half and Harry Wilson twice went close to doubling their lead, before late substitute Mason Greenwood hit the post moments after coming on for United.
But the visitors could not prevent Bournemouth securing their first win in six, which sent them back above the Red Devils to sixth before the rest of Saturday's games.
Martial not the answer to all United's problems
Having gone unbeaten since the international break, holding league leaders Liverpool before claiming three straight wins for the first time this season, United fans hoped the club had turned a corner.
Manager Solskjaer felt confidence was building and Anthony Martial's return to the side for last week's win at Norwich looked to have revived the United attack. After all, the Red Devils had won 65% of their games with Martial starting under Solskjaer, compared to 41% without.
After winning at Chelsea in the Carabao Cup, Solskjaer reverted to last Sunday's starting line-up, but his side failed to show the same fluency, particularly Martial and strike partner Marcus Rashford.
Instead their biggest threat was Daniel James, who created two early chances from the right. Andreas Pereira blazed over while fellow Brazil midfielder Fred scuffed a shot wide.
James then won a free-kick which led to the Wales winger firing narrowly wide from 20 yards, and as United struggled to maintain that early dominance, King pounced.
The 27-year-old striker was left unmarked before Wan-Bissaka committed himself, allowing the Norway international to control the ball on his chest, flick it over his head and hammer past De Gea.
The Spanish keeper kept United in it with a string of saves after the break, before Solskjaer made a double substitution, bringing on Greenwood and Brandon Williams with 10 minutes left.
Greenwood volleyed Fred's cross against the woodwork at the back post before Scott McTominay and Fred tested home keeper Aaron Ramsdale from outside the box, but those chances came more through desperation than design.
Cherries end goal drought
While Bournemouth conceded just one goal in three games in October they also failed to score, but manager Eddie Howe backed his attacking players in Friday's news conference and made only one change to the side which drew 0-0 at Watford.
Harry Wilson came in and the Liverpool loanee had the Cherries' first shot, which was deflected wide, before a Bournemouth break saw Ryan Fraser shoot straight at De Gea.
Yet the Cherries seldom managed to get behind the visitors' defence until Harry Wilson and Fraser combined to find Smith in the right side of United's box. The full-back lifted the ball towards King, who showed great composure to convert his fourth goal of the season.
After the break Bournemouth looked more like the side which went third in the table after a 3-1 win at Southampton on 20 September.
Fraser steered a volley straight at De Gea, who had to rush out to deny King and Harry Wilson in quick succession.
De Gea then had to produce a fine low save to keep out Harry Wilson's left-footed strike before ever-present keeper Ramsdale made two late saves to ensure the Cherries kept a third straight clean sheet.
'We fully deserved to win' - what they said
Bournemouth manager Eddie Howe: "Today we were much more like ourselves with the ball and also very determined without the ball.
"We managed to keep three clean sheets in a row so I am really pleased with that and the attacking play was back today so I think we fully deserved to win.
"These results could be season defining. In our previous Premier League campaigns we have beaten top teams and we know what these results can do for our confidence in the longer term."
Manchester United manager Ole Gunnar Solskjaer: "You are always very down when you lose and considering the form we were in we were hoping to take the three points.
"We could not capitalise on the good start and a moment of magic won the game for them, sometimes you just hold up your hands and say 'well done'.
"I thought Marcus Rashford and Anthony Martial defended very well against them, but in games like this one it is so important to get the first goal and they [Bournemouth] did it.
"We are disappointed but when you come to places like this you have to take control of the game. We did not and we could not get the goal. We were missing some quality at times. Maybe I should have started some others."
King second only to Solskjaer - the stats
- Manchester United have lost all six Premier League away games in which they've fallen behind under Ole Gunnar Solskjaer.
- United have failed to keep a clean sheet in any of their last 11 Premier League away games.
- Bournemouth ended a seven-match winless run against United in the Premier League (D1 L6), picking up their first win against the Red Devils since December 2015.
- Six of Bournemouth's eight Premier League victories against 'big six' opposition have come at Vitality Stadium.
- Joshua King netted the 45th Premier League goal of his career - the second-highest total by a Norwegian player in the competition's history after United manager Solskjaer (91).
- Since the start of last season no player has been shown more yellow cards than Bournemouth's Jefferson Lerma (17).
- Bournemouth's four wins this season have come from the five games in which they've had the least amount of possession (42.5% v United).
Man of the match - Steve Cook (Bournemouth)
Manchester United have a Europa League group game at home to Partizan Belgrade on Thursday (20:00 GMT) before hosting Brighton in the Premier League next Sunday (14:00), while Bournemouth visit Newcastle next Saturday (15:00).
- 15A Smith
- 3S CookBooked at 55mins
- 22WilsonSubstituted forL Cookat 86'minutes
- 8LermaBooked at 35mins
- 24FraserBooked at 62mins
- 13WilsonBooked at 90mins
- 14Danjuma Groeneveld
- 16L Cook
- 1de Gea
- 29Wan-BissakaSubstituted forWilliamsat 81'minutes
- 2LindelöfBooked at 64mins
- 18YoungBooked at 67mins
- 17FredBooked at 35mins
- 21JamesSubstituted forGreenwoodat 80'minutes
- 15PereiraSubstituted forLingardat 68'minutes
- Chris Kavanagh
- Shots on Target
Second Half ends, Bournemouth 1, Manchester United 0.
Attempt saved. Fred (Manchester United) left footed shot from outside the box is saved in the centre of the goal. Assisted by Jesse Lingard.
Callum Wilson (Bournemouth) is shown the yellow card.
Callum Wilson (Bournemouth) has gone down, but the referee deems it simulation.
Attempt blocked. Scott McTominay (Manchester United) right footed shot from outside the box is blocked. Assisted by Brandon Williams.
Attempt missed. Harry Maguire (Manchester United) header from the centre of the box misses to the right. Assisted by Ashley Young with a cross following a corner.
Corner, Manchester United. Conceded by Diego Rico.
Brandon Williams (Manchester United) wins a free kick in the defensive half.
Foul by Joshua King (Bournemouth).
Substitution, Bournemouth. Lewis Cook replaces Harry Wilson.
Offside, Manchester United. Jesse Lingard tries a through ball, but Harry Maguire is caught offside.
Corner, Manchester United. Conceded by Steve Cook.
Foul by Harry Maguire (Manchester United).
Adam Smith (Bournemouth) wins a free kick in the defensive half.
Scott McTominay (Manchester United) wins a free kick in the attacking half.
Foul by Ryan Fraser (Bournemouth).
Attempt saved. Scott McTominay (Manchester United) right footed shot from outside the box is saved in the centre of the goal. Assisted by Fred.
Mason Greenwood (Manchester United) hits the right post with a left footed shot from the right side of the six yard box. Assisted by Fred with a cross following a corner.
Corner, Manchester United. Conceded by Adam Smith.