The Chile international struck in controversial circumstances in the fourth minute at Wembley, taking him to 30 goals in all competitions for the 2016-17 campaign.
It was the first time since the Dutchman's 2011-12 campaign that an Arsenal player reached the mark. Overall, Sanchez has been involved in an impressive 45 goals in 51 appearances for Arsenal this season.
Sanchez's goal was also the fastest ever strike for the Gunners in an FA Cup final, notched with 3:49 on the clock.
The Gunners won the match 2-1 thanks to Aaron Ramsey's late winning, clinching their third FA Cup title in four seasons.