Claude Puel's side, defending a 1-0 lead from the first leg, should have put the tie out of Liverpool's reach inside the first 45 minutes but Dusan Tadic's close-range shot was blocked by keeper Loris Karius and captain Steve Davis blazed another great chance wildly over.

Liverpool raised the tempo in front of the Kop in the second half but Daniel Sturridge wasted their two best chances, Fraser Forster acrobatically hooked an Emre Can shot off the line and the hosts also had a late penalty appeal turned down when substitute Divock Origi tumbled under Jack Stephens' challenge.

But Southampton broke clear in the closing moments and Long finished convincingly from Josh Sims' pass to send them into the their first final in this competition since 1979, where they will meet either Manchester United or Hull City - a feat achieved without conceding a goal.