Arsenal made it 3-0 when Koscielny bundled the ball in. His team gave the ideal response to the testing period though as they raced into a four-goal lead to wrap up the match inside 22 minutes.
Despite Arsenal's woes, Palace boss Roy Hodgson believes the vilification of Wenger is unjustified.
Arsenal: Petr Cech 7 (out of 10), Hector Bellerin 7, Laurent Koscielny 7, Shkodran Mustafi 7, Nacho Monreal 8, Granit Xhaka 6, Mohamed Elneny 7, Jack Wilshere 7, Mesut Ozil 8, Alex Iwobi 7, Alexandre Lacazette 7.
Arsenal took their foot off the gas after the restart and Palace netted a consolation through Luka Milivojevic on 78 minutes, but the day belonged to the home side's free-flowing football.
United are reportedly set to part with £35million, plus Henrikh Mkhitaryan, to secure Sanchez's signature, although Jose Mourinho insisted on Friday that the deal was "not done at all". Not exactly a butchers' row of opponents, and even their match against Chelsea was marred by neither team really seeming to want to play in the 0-0 draw.
The cut-off time for the duo to be able to be registered in time for the weekend's Premier League fixtures against Burnley and Crystal Palace respectively has just passed with neither player having been confirmed, and it would be a disgusting thought that it could be mostly down to the fee of the agents which has stopped us from being able to field the Armenian this weekend.
The win is Arsenal's first in 2018 and keeps them in sixth.