Having won each of the last six home games against West Brom, Arsenal fans were probably expecting another routine victory over the Baggies on Monday night.
But it was anything but routine. Arsenal were lucky to not concede a penalty in the opening stages when Shkodran Mustafi brought down Jay Rodriguez inside the 18-yard box.
Referee Bobby Madley, somehow, didn't point to the spot.
Alexandre Lacazette then opened the scoring with a typical poacher's finish in the 20th minute when Alexis Sanchez's free-kick was parried by Ben Foster.
Lacazette's header was his third goal in as many home games for his new club to continue his bright start in north London.
It proved to be the only goal of the opening 45 minutes, but West Brom had their chances.
Nacho Monreal cleared off the line from Grzegorz Krychowiak's header before Rodriguez saw his goal-bound effort blocked by Mustafi.
Safe to say more was needed from Arsenal if they were to secure all three points.
Arsene Wenger will have told his players to cut out the silly mistakes in the dressing room having given away possession cheaply on a number of occasions.
Change was needed, but no one could quite believe their eyes when Arsenal reappeared from the tunnel for the second period.
In the video below, as Arsenal's players walked onto the pitch, they performed a weird little cone routine before running into their positions (see below).
ARSENAL'S CONE ROUTINE
What on earth was that? Do Arsenal's players really need to run in and out of cones at half-time to keep themselves warm? Surely not.
Football fans found it pretty stupid regardless, as you can see in the following Twitter reaction.