Arsenal defeated Chelsea 2-1 on Wenesay at the Emirates Sports Stadium to set a date in the Carabao Cup final with Manchester City
After a goalless first leg, Eden Hazard put Chelsea ahead before an own goal from Antonio Rudiger levelled it, and Granit Xhaka's winner took Arsenal to Wembley.
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It came only two days after Sanchez's drawn-out transfer to Manchester United was completed, with the Gunners getting Henrikh Mkhitaryan in return.
A miserable couple of months for Arsenal has seen them drop to sixth in the Premier League, 23 points behind leaders Manchester City, and lose to Championship Nottingham Forest in the FA Cup.
But now this vital victory keeps them on course to win their fourth trophy in five years - and with it claim the only domestic competition that Arsene Wenger has not won in his 21 years at the club.