Petr Cech’s awful mistake and two goals from Sam Clucas condemned Arsenal to a shock 3-1 defeat at Swansea on a day new signing Henrikh Mkhitaryan made his debut for the club.
The Armenian, who joined in a swap deal that saw Alexis Sanchez move to Manchester United, replaced Mohamed Elneny in the 60th minute.
But Mkhitaryan had little effect on proceedings as the host produced another impressive display.
Arsenal goalkeeper Cech horribly miscued an attempted clearance that allowed Jordan Ayew to give Swansea a crucial 61st-minute lead.
Nacho Monreal had put Arsenal 1-0 up, but Clucas levelled before the midfielder sealed the victory with Swansea’s third goal in the 86th minute.
The result leaves Gunners manager Arsene Wenger still searching for his first away win of 2018.
Arsenal have won only one of their last five league games.
With Liverpool winning at Huddersfield, sixth-placed Arsenal are now languishing eight points adrift of the top four, leaving them with an uphill task to qualify for next season’s Champions League.
The arrival of Borussia Dortmund striker Pierre-Emerick Aubameyang, set to sign on Wednesday’s transfer deadline day, can’t come soon enough for Wenger.
The result also completes remarkable back-to-back victories for Swansea, who have transformed their season with three wins in five league games under new boss Carlos Carvalhal.
