Arsenal dominated the ball in the first half and took the lead through Shkodran Mustafi.
However, Palace were much improved after the break and they found a leveller with just four minutes of the second half gone.
Wilfired Zaha left Calum Chambers for dead down the left before crossing low and Townsend was on hand to drill the ball home first time.
It was a sharp finish from the England international, who could barely hide his delight.
Check out the strike for yourself below:
Goal - Townsend scores vs Arsenal, Assisted by Zaha - 1-1 pic.twitter.com/7ROOxqTV2W
— ArsenalUpdates (@ArsenalEdits___) 28 December 2017