Arsenal slumped to a shock 1-0 defeat at Sheffield United as Lys Mousset condemned the Gunners to their latest away-day flop on Monday.
Unai Emery’s side are without an away Premier League win since the opening weekend of the season after failing to rise to the challenge posed by fired up United at Bramall Lane.
French forward Mousset, making his first Premier League start for United, punished poor Arsenal defending in the first half to score his second goal since signing from Bournemouth.
That was enough to send Arsenal crashing to just their second defeat of the season, ending an eight-game unbeaten run in all competitions.
The north Londoners sit fifth in the league after a powder-puff performance that showed Emery’s rebuilding job is still a work in progress.
Under Emery, Arsenal have kept just two clean sheets in 24 away league matches and once again they wilted too easily in a hostile environment.
This was a signature win for the Blades after last season’s promotion and they sit proudly in ninth place, just three points behind Arsenal.
With the Bramall Lane crowd in full voice, a bruising clash got off to a contentious start when Arsenal defender Sokratis appealed in vain for a penalty after having his shirt tugged by John Egan.
United midfielder John Fleck was fortunate to escape with a yellow card from referee Mike Dean after crunching into Pierre-Emerick Aubameyang.
Emery’s men should have taken the lead when Sead Kolasinac curled a perfect low cross towards Nicolas Pepe in the six-yard box, but the unmarked Ivory Coast winger completely miscued his shot.
It was the latest in a growing list of disappointing displays from Pepe, who has struggled to make an impact since his club record move from Lille in the close-season.
United made the most of that escape as Arsenal’s long-running set-piece issues resurfaced in the 30th minute.
Oliver Norwood’s corner reached Jack O’Connell at the far post and he rose above Matteo Guendouzi to head down to Mousset, who poked home from virtually on the line after Granit Xhaka failed to react to the danger.
Damningly, Arsenal have conceded 22 league goals from set plays since the start of last season, with only Watford (25) and Everton (24) allowing more.
Bukayo Saka tried to lead the Arsenal response with a surge into the United area, but the teenager went to ground too easily and earned a booking for diving.
Xhaka almost conjured an equaliser with a dipping long-range effort that Dean Henderson pushed away at full stretch.
Mesut Ozil was once again left out of the Arsenal squad and, with Aubameyang anonymous, Emery sent on Dani Ceballos for Joe Willock at half-time for an injection of creativity.
The on-loan Real Madrid midfielder should have equalised when he shot weakly at Henderson from Saka’s cross.
Always creaky at the back, Arsenal were nearly caught when Fleck thudded into the side-netting and then forced Bernd Leno into an unconvincing save.
Alexandre Lacazette came on with 22 minutes left for his first appearance since suffering the ankle problem that had ruled the Arsenal striker out since the start of September.
For all their territorial dominance in the closing stages, Arsenal lacked composure in the final third.
Pepe curled just wide and Kolasinac headed over as the visitors’ frailties were laid bare.