A flying start was not enough to secure three points as we lost further ground in the Premier League.
Goals from each of our centre backs in the space of 106 seconds had given us a solid foundation to go on and win this game.
Sokratis - marking his 50th appearance - thumped in the first after Palace failed to clear Pepe's corner. And David Luiz converted the second from close range after another Pepe corner was headed on by Alex Lacazette.
We didn't create that much in open play but we looked pretty secure until the match turned on a VAR decision.
Wilfried Zaha went down under a challenge from Calum Chambers inside the box and was initially booked for simulation. But replays suggested Zaha should have had a spot kick and the decision - and the yellow card - were overturned.
Luka Milivojevic is ruthless from 12 yards and hauled Palace back into the game with a minimum of fuss. And their comeback was complete when James McArthur got down the left and clipped over a cross for Jordan Ayew to apply a simple finish.
We regrouped and pressed for a winner, and looked to have got it when Sokratis blasted in after yet another corner.
The celebration was long and loud, but VAR intervened again and the goal was disallowed.
HOW IT HAPPENED
THREE THINGS WE NOTICED
WHAT IT MEANS
Unai Emery made nine changes from our win over Vitoria - and handed Kieran Tierney his Premier League debut.
The Scotland international was one of two players to keep their place, with Alex Lacazette retained up front. He lined up alongside Pierre-Emerick Aubameyang and Pepe.
Joe Willock and Mesut Ozil were left out of the squad.
The Carabao Cup returns in midweek and that means a second trip of the season to Anfield to face Liverpool.
Our next Premier League game is a home one, against Wolves next Saturday.
Copyright 2021 The Arsenal Football Club plc. Permission to use quotations from this article is granted subject to appropriate credit being given to www.arsenal.com as the source.