Arsenal will hope to seal deals for Henrikh Mkhitaryan and Pierre-Emerick Aubameyang in the transfer window, but neither has been completed yet.
The return of German playmaker Mesut Ozil, who laid on a lovely backheeled assist for Lacazette's goal, also helped Arsenal fans to forget the absence of Sanchez, who was left out of the squad for a second straight game.
It was also vital to Arsenal's chances of qualifying for next season's Champions League as they move within five points of fourth-placed Liverpool.
Jack Wilshere teed up Ozil and his sublime back-heel sent France striker Lacazette clear to slot home his first goal in his last 10 appearances.
Luka Milivojevic swivelled to drive in Palace's consolation in the 78th minute, but the damage was long since done.
Four minutes later it was 2-0 as a loose clearance was picked up by Monreal and his ball in from the left was converted from close range by the arriving Alex Iwobi.
But that was the only sour note on an otherwise excellent outing for the Gunners ahead of their crucial EFL Cup semi-final date with Chelsea, while Palace's poor day at the office took another bad turn when Yohan Cabaye left the pitch on a stretcher in the final moments.
After putting his name on the score-sheet in Arsenal's dismantling of Crystal Palace yesterday in their English Premier League match, Alex Iwobi has called for more consistency from the Gunners.
- Roy Hodgson is now winless in all 11 of his Premier League away London derbies as manager (D3 L8).
Palace, meanwhile, enjoyed a run of eight games without defeat before losing to Arsenal.