Wenger was naturally questioned and the Gunners boss confirmed that the 29 year old forward is now on his way to Manchester United.
Wenger said the move wasn't yet "over the line".
As Sanchez prepares to seal a £30 million switch that will reportedly see United midfielder Henrikh Mkhitaryan move to Arsenal as part of the deal, and possibly also prompt Wenger to sign Borussia Dortmund striker Pierre-Emerick Aubameyang, this was a well-timed reminder that the Gunners still have some talent in reserve.
Monreal scored Arsenal's first goal five minutes in, then provided assists for Iwobi's 10th-minute goal and Koscielny's 13th-minute goal.
The win keeps Arsenal in sixth, but they cut the gap on Tottenham in fifth place to two points before Spurs visit Southampton on Sunday.
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After spluttering badly in recent weeks Arsenal were sweeping forward with real objective and doubled their lead in the 10th minute.
Palace were in complete disarray and Wenger's men punished more woeful defending to make it three in the 13th minute.
Palace failed to learn its lessons, however, as another Xhaka set-piece was met at the far post by Monreal, whose ball across was bundled home by Koscielny inside the six-yard box. The Germany worldwide was heavily involved in all of Arsenal's slick interplay in the opening period and capped his performance with a sensational assist before being given a deserved rest with 18 minutes remaining.
Ozil exchanged passes with Jack Wilshere and upon receiving the return, flicked a sumptuous backheel into the path of Lacazette, who swept home first-time into the bottom-right corner.
Crystal Palace: Wayne Hennessey 5, Timothy Fosu-Mensah 6, Martin Kelly 5, James Tomkins 6, Patrick Van Aanholt 6, Yohan Cabaye 6, James McArthur 5, Luka Milivojevic 6, Wilfried Zaha 6, Bakary Sako 5, Christian Benteke 6.