Arsenal got off to a great start on six minutes as Nacho Monreal headed in unmarked at the back post from Granit Xhaka’s corner.
Iwobi doubled Arsenal’s lead in the 10th minute, slotting home Monreal’s cutback in a crowded Palace box.
Laurent Koscielny got on the score sheet to make it 3-0 in the 13th minute as he tapped in another cutback from Monreal from a corner.
Arsenal continued to press and scored a fourth, this time through Alexandre Lacazette who hit a low shot past Palace keeper off a brilliant back-heel pass from Mesut Ozil after a brilliant interchange of passes.
Palace pulled a goal back on 77 minutes through Luka Milivojevic who chested a flick from a corner and smashed the ball into net.
Despite the win, Arsenal still remain sixth on 42 points in the league table.
At the King Power Stadium, Super Eagles midfielder Wilfred Ndidi returned to Leicester City starting eleven as they beat Watford 2-0. He was rested for the FA Cup replay against Fleetwood Town in midweek.
Leicester’s goals were scored by Jamie Vardy on 39 minutes from the penalty spot and a 90th minute strike from Riyad Mahrez.Jamie Vardy scored the only goal from the penalty spot on 39 minutes after he was fouled inside the box.
The win means Leicester now occupy the seventh position on 34 points on the log.
At Turf Moor, Manchester United pipped Burnley 1-0 to go seven straight games without defeat in all competitions.
Anthony Martial got United’s only goal in the 54th minute with a brilliant strike from a Romelu Lukaku assist.
The win means United stay second on 53 points and are now temporarily nine points behind leaders Manchester City.
And in other Premier League results, Theo Walcott made his debut for Everton who were held to a 1-1 home draw by West Brom, West Ham played 1-1 with visiting Bournemouth, while Stoke beat Huddersfield 2-0 at the Bet 365 Stadium.
Arsenal 4 vs 1 C/Palace
Leicester 2 vs 0 Watford
Burnley 0 vs 1 Man United
West Ham 1 vs 1 Bournemouth
Stoke 2 vs 0 Huddersfield
Everton 1 vs 1 West Brom