Arsenal beat Reading in extra-time to reach FA Cup Final
Sanchez gave the Premier League side a 43rd-minute lead from close range before Garath McCleary volleyed home an equaliser shortly after the break.
Reading needed the post and keeper Adam Federici to keep the scores level as the game needed an extra 30 minutes to decide the outcome.
The Australian keeper was at fault as Sanchez's effort spilled through his grasp and in and although Reading pushed for an equaliser Arsenal held on.
The Gunners will now face the winners of Sunday's other semi-final between Aston Villa and Liverpool as they look to lift a record 12th FA Cup.