The Frenchman took charge of his 811th Gunners league game, taking him past Alex Ferguson's Premier League record of 810.
The Gunners looked to be headed for three points until Dean stepped in, with Jay Rodriguez equalising from the spot following an alleged handball in the Arsenal penalty box to force a 1-1 draw.
No West Brom player has provided more assists (2) or created more goalscoring chances (21) in the Premier League this season than Chris Brunt, this despite the Northern Ireland midfielder making just 10 appearances.
And Iwobi's left-footed drive was clawed around the post by Foster on the half-hour mark, before the Arsenal youngster was fouled by Jonny Evans, who received the first booking of the night. It's more the decision involved in that and it's not the first time.
Arsenal's small adjustment to their kit for today's match against West Brom has got people talking. Foster stuck a leg out to make a good save.More news: Diego Costa reflects on his time at Chelsea
Alexandre Lacazette then saw a shot deflected inches wide at the other end, and a game that had started sluggishly began to show some promise.
But when the former Chelsea stopper walks away, he can be seen mouthing "f****** c***" as he storms back towards the tunnel.
But with seven minutes remaining the dam was breached as Arsenal took the lead with a free-kick won and converted by Sanchez. "The level of the referees unfortunately doesn't go up".
Sky Sports pundit Gary Neville felt the decision was extremely harsh in commentary and Wilshere was booked for dissent, while word also came through that Arsenal's goal had been credited to McLean, not Sanchez.
And Wenger says Dean made the wrong decision and it cost Arsenal.
For the first time in almost 40 years, Arsenal will wear red shorts with their home strip against West Brom tomorrow.