Arsenal remain on course for a record 13th FA Cup triumph after battling back from a goal down to beat Manchester City 2-1 after extra time at Wembley Stadium.
The Gunners trailed to a Sergio Aguero goal heading into the final quarter of the game, but Nacho Monreal fired home to take the game the distance and Sanchez proved the hero in the 101st minute.
City hit the frame of the goal twice in the latter stages of the contest and had a goal incorrectly ruled out in the first half, but for the first time in nine appearances at this stage of the competition they came out second best in the end.
Both sides managed just one shot on target in the opening 45 minutes, coming in the space of 60 seconds as Olivier Giroud aimed a header straight at Claudio Bravo at one end and Silva denied by Petr Cech at the other – his last involvement in the match.
Nicolas Otamendi nodded into the ground and wide from a corner early in the second period and Sanchez was so nearly in following Bravo’s slip, but the breakthrough moment did eventually arrive shortly after the hour.
Arsenal gave away possession through Aaron Ramsey and, a Yaya Toure ball over the top later, Aguero was clean through on goal and dinking it over Cech after his initial first touch tempted the Czech to race out.
A 12th goal in 12 outings for Aguero gave City, who lead the Gunners by seven points in the Premier League after playing one game more, something to hold onto in the remaining 30 minutes.
Hold on they could not, though, as the Gunners – competing at this stage for a 29th time – levelled up soon after when their two wing-backs combined to justify Arsene Wenger’s big gamble.
Oxlade-Chamberlain swung in a delightful cross from the right, which was met emphatically by Nacho Monreal at the back post with a right-footed volley past Bravo.
As the minutes ticked towards extra time, substitute Danny Welbeck decided against picking out Ramsey and instead attempted to whip the ball into the far corner, missing by a matter of inches in a thrilling end-to-end conclusion.
Sanchez bagged his fourth goal in three appearances at Wembley, prodding home when Ozil’s free kick into the box fell into his path to send Arsenal through to an FA Cup final meeting with London rivals Chelsea in five weeks’ time.