Palace were trailing after Mohamed Salah had won a debatable penalty in the first half, which James Milner converted, and the Player of the Year from last season was again involved in a turning point in the game.
Wan-Bissaka had played well all game, and recognised that Salah was running in on goal and went to try and challenge the forward.
With the Liverpool man just outside the box, the two made contact and Salah fell to the ground.
Referee Michael Oliver did not hesitate, and immediately gave the full-back his marching orders.
The Liverpool tallisman could only hit the resulting free-kick in to the wall, much to the delight of the home fans who gave Wan-Bissaka a standing ovation as he left the pitch.