Swansea climbed out of the relegation zone for the first time in three months as Petr Cech's dreadful clanger condemned Arsenal to a 3-1 defeat at the Liberty Stadium.
Cech's scuffed kick gifted Jordan Ayew a simple finish in the 61st-minute winner after Sam Clucas had put Swansea on level terms, instantly cancelling out Nacho Monreal's first-half opener.
Clucas claimed his second three minutes from time to finish off Arsenal, who hope to add to their squad before Wednesday night's transfer deadline with Pierre-Emerick Aubameyang set to swell their striking options.
But the Borussia Dortmund forward would not have been impressed with his new team-mates, who did not manage a goal attempt in the opening half-hour and were often second best against the Swans.