Arsenal were looking to bounce back from a shock 2-1 defeat to Bournemouth on Sunday and Arsene Wenger's side did just that by scoring three goals in the first 13 minutes at the Emirates.
Monreal was involved in all three, scoring one and providing two assists. His header from the far post stole the lead for the London club in the fourth minute.
Two minutes later, Iwobi made it 2-0 with an easy enough finish after Monreal cut the ball back from the left-hand side.
To compound Palace's misery, Koscielny made it 3-0 in the 13th minute with an easy tap-in after the Spanish left-back connected with a cross at the back post to tee it up perfectly for his Arsenal team-mate.
Check out the goals for yourself below:
Monreal 1-0:
January 20, 2018
Iwobi 2-0:
20 January 2018
Koscielny 3-0:
January 20, 2018