Arsenal's stuttering away form in the Premier League continued as Lys Mousset's first-half strike gave Sheffield United a 1-0 win on Monday Night Football.
Sheffield United were the better side at Bramall Lane and their victory was ultimately sealed when Mousset - making his first Premier League start for his new club - tapped home in the 30th minute.
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Arsenal - who are unbeaten at home this season - have now lost two and drawn two of their last four away games in the league and the defeat brings their eight-game unbeaten run to an end, keeping them in fifth place in the table.
For Sheffield United, the result will go down as a famous win and they have jumped from 15th into ninth with 12 points from nine matches - level with Bournemouth, Burnley and Tottenham.
How the Blades picked up famous win
Sheffield United began the game well, but it was Arsenal who had the first real chance in the 21st minute. Nicolas Pepe began the superb passage of build-up play, that culminated in an inch-perfect cross from Sead Kolasinac that the Ivory Coast winger could not convert at point-blank range.
But the Blades made their good play count on the half-hour mark when they took the lead. It was a routine straight off the training ground too as Oliver Norwood's deep corner was headed back across goal by Jack O'Connell and tapped home by Mousset, who was finding the net at Bramall Lane for the first time.
Sheffield United: Henderson (7), Baldock (7), Basham (7), Egan (8), O’Connell (8), Stevens (7), Lundstram (7), Fleck (8), Norwood (7), McGoldrick (6), Mousset (7).
Subs used: Sharp (6), Freeman (5), McBurnie (n/a).
Arsenal: Leno (6), Chambers (6), Sokratis (6), Luiz (6), Kolasinac (7), Guendouzi (7), Xhaka (5), Willock (5), Saka (6), Aubameyang (6), Pepe (6).
Subs used: Ceballos (7), Lacazette (7), Martinelli (5).
Man of the match: John Fleck.
Arsenal had a glorious chance to equalise just before half-time, but were thwarted by a stunning Dean Henderson save. Granit Xhaka thundered a shot his way from distance, but the goalkeeper arrowed towards the top corner to keep him out.
In the opening 20 minutes of the second half, United had a few chances to double their lead. George Baldock sliced a shot wide before John Fleck's effort from 25 yards skimmed the side of the net.
- Sheffield United made two changes up front. Oli McBurnie and Callum Robinson started on the bench and were replaced by Lys Mousset, making his first Premier League start, and David McGoldrick.
- Arsenal made one change with Joe Willock replacing Dani Ceballos in the starting line-up.
Fleck was trying his luck again not long after as his effort from range went straight at Bernd Leno, but he was unable to hold the initial shot and had to pounce on the loose ball with David McGoldrick storming in to slot home.
Pepe could have been Arsenal's hero towards the end as he had two good chances in quick succession. The first in the 73rd minute was a free-kick which Henderson saved well before he shot just wide of the post a minute later.
But the Gunners were not able to find a way past a resolute home defence as the Blades picked up a famous victory.
What the managers said
Sheffield United manager Chris Wilder: "For the club to host a game like this, the magnitude of it - to play well and get a win is massive. We came under pressure in the second half but we limited them to a few chances and we backed up a good performance with a good result.
"We played well a few weeks ago against the European champions [Liverpool], and so we knew we could get something from the game. It's crazy to think we could just open up against Arsenal, and they showed that in the first half.
"We had to get the balance [right] in and out of possession and I feel we did that. Dean's made a couple of saves but we've had a couple of chances in the second half too and I feel we deserved to get something.
"It's not the biggest result in the club's history but it's a fantastic one and a great reward for everybody as it's been quite a difficult journey to get here."
Arsenal manager Unai Emery: "I feel we didn't deserve to lose. We conceded a lot of corners in the first half, and they scored their goal in one of these actions. But, above all, we conceded that corner too easily.
"From an offensive point of view, we created more chances than them. We knew here it would be tough because they haven't conceded many goals in the Premier League, especially after they took the lead. They defended well.
"There were two key moments in the match: one was their goal, and the second was a very clear penalty for us for a foul on Sokratis. It was very clear."
Patrice Evra told Monday Night Football: "Sheffield United deserved the win, but I'm not surprised about Arsenal. I said before the game that they had to make sure they didn't fall into the trap.
"I used to call them 'my babies' 10 years ago, and they are still when I look at them and think they are 'my babies' and that's the truth - I'm not being disrespectful when I say that.
"They look pretty, but they don't look like a winning team. They like playing good football, but I was so happy to play against them, because I knew I was going to win.
"Guendouzi was playing in midfield, but before he was playing in the French second league and he was not even playing regularly - and he's the best player in this team.
"I respect Aubameyang and Lacazette, but if those two guys don't score, they're in trouble, and nothing changes. I'm like, 'where is Arsene?'. It is the same."
Man of the match - John Fleck
Fleck was the driving force behind a Sheffield United attack that gave Arsenal some real problems. He had the most shots (2 - one on target), crosses (6) and key passes (3) of any home player.
He had the joint-second highest number of touches (51) and made 28 passes in the opposition half - again, the best of the Blades. He had a real hand in the win and should be proud of his performance.
- Arsenal have played more Premier League games at Bramall Lane without victory than they have any other ground in the competition (4 - D2 L2).
- Since the start of last season, Arsenal have been shown more cards for diving than any other Premier League team (7).
- Sheffield United's Dean Henderson has kept 25 clean sheets in the league since the start of last season; more than any other goalkeeper in England's top four tiers.
Arsenal host Vitoria Guimaraes at 8pm on Thursday in the Europa League, before facing Crystal Palace in the Premier League on Sunday; Kick-off 4.30pm.
Up next for Sheffield United is a trip to the London Stadium to face West Ham on Saturday; Kick-off 3pm.