A goal after just 44 seconds had left the Gunners playing catch-up for most of the game, Edinson Cavani heading Serge Aurier’s cross past David Ospina before some fans had taken their seats.
Cavani should have had more, missing an open goal in the first half, and Ospina kept Arsenal in the game with a string of fine saves after the break.
The visitors kept plugging away and their patience in possession was eventually rewarded when Alex Iwobi’s shot was pushed out by Alphonse Areola and Alexis rifled in the rebound.