Victor Moses put Chelsea ahead shortly after play resumed following the half-time break.
But Pedro got himself sent off for a nasty challenge on Mohamed Elneny 10 minutes before the end of the match.
And Sead Kolasinac headed in an equaliser just seconds later to send the game to a penalty shoot-out.
It was the Arsenal players who kept their nerve to win the Community Shield after Thibaut Courtois and Alvaro Morata both missed their spot kicks with the shoot-out using the new ABBA format.
Arsene Wenger will be delighted his side managed to get a confidence-boosting win in their first proper game of the season.
And their fans took to Twitter after the game to praise their side and celebrate the win.
Click through the gallery above to see some of the best reaction from Arsenal fans.
