Arsenal missed out on the chance to move up to third place in the Premier League as they fell to a 1-0 defeat against Sheffield United on Tuesday (AEST)
Unai Emery's men entered the match unbeaten in eight matches, including five in the top flight, but came unstuck at Bramall Lane.
The only goal of the game was scored by Lys Mousset half an hour in, coming shortly after Nicolas Pepe had failed to round off a swift counter.
Arsenal had a strong penalty appeal turned down and ultimately could not find a way through, leaving them fifth in the table and winless in four league visits to this ground.
The visitors were punished for Pepe's close-range miss by Mousset's opener eight minutes later.
Jack O'Connell headed down a corner into the six-yard box, where Mousset was waiting to pounce to double his tally for the season.
The visitors were further frustrated when Bukayo Saka was cautioned for simulation when he went down in the box, despite arguing that contact was made by Enda Stevens.
Granit Xhaka had a long-range drive pushed aside by Dean Henderson and the same player glanced over just before half-time.
Pepe was also denied by Henderson from a free-kick and Sead Kolasinac headed over from a good position, but Arsenal were unable to find an equaliser on another day of frustration for Emery.
What does it mean? Away-day blues costing Arsenal
Arsenal are now winless in four Premier League away games since beating Newcastle United on the opening weekend, losing two and drawing two - an issue Unai Emery quickly needs to rectify.
The Gunners have also kept only two clean sheets in 24 top-flight matches on their travels, with this latest setback denying them the chance to move into the Champions League places.
Norwood takes control
Oliver Norwood has impressed during the early stages of the season and produced another composed display here.
He completed 34 passes - more than any other home player - and nobody could better his five tackles.
Pepe's miss proves costly
Arsenal's defence will understandably be criticised after conceding from another set-piece - only Watford and Everton have conceded more from those situations since the start of last season - but their attack also needs sorting.
Pepe squandered a glaring opportunity to put the visitors in front shortly before Mousset's opener and managed just one shot on target all match.
Arsenal take on Vitoria Guimaraes in the Europa League on Thursday, before returning to league action with a home match against Crystal Palace on Sunday. Sheffield United have a five-day break prior to facing West Ham.