The Gunners ended a five-match winless run in all competitions and tasted victory for the first time in 2018 thanks to their incredible goal blitz at the Emirates Stadium.
Sanchez's firepower was not needed against an out-of-sorts Palace, which went behind after six minutes when Monreal headed in a corner by Granit Xhaka.
Arsenal will hope to seal deals for Henrikh Mkhitaryan and Pierre-Emerick Aubameyang in the transfer window, but neither has been completed yet.
However, only Man City (31) and Man Utd (29) taken more Premier League points at home this season than Arsenal, so Palace will be well aware of the tough task ahead.
- MR DT © (@MrDtAFC) January 20, 2018I'm expecting @Arsenal players to roll their sleeves up today and say "We love our club and to hell with those who no longer what to be part of us".
Paul Pogba's evolution with United encourages Jose Mourinho
City would need a huge collapse and United would need a near-perfect second half of the season with 15 games remaining. It's good that they lose points but we have to go back to winning because we want to catch them again.
"We have been playing the sort of football you saw in the second half and the fact we can do that against a team of Arsenal's quality pleases me". Suddenly Wenger is searching the back of the cupboard.
Wilshere picked up the ball in plenty of space and fed Ozil, whose deft flick was ideal for Lacazette to slot home his first goal since the 3-1 defeat to Manchester United on December 2.
Despite only one loss from their last 12 Premier League fixtures, Palace could find themselves being beaten twice in 23 days by the Gunners after they travel to North London this weekend.
From the resulting set-piece, Monreal powered past Palace's sloppy marking to head home from close-range.
Crystal Palace manager Roy Hodgson has admitted that his side were "staring down the barrel of the gun" when trailing Arsenal by four goals at half time on Saturday afternoon.
Arsenal made it 3-0 when Koscielny bundled the ball in.