The Reds suffered a setback in their bid to reach the final for the 12th time in the competition after Marko Arnautovic broke the deadlock on the stroke of half-time.
The former Inter Milan midfielder’s equaliser cancelled out Jordon Ibe’s winner in Liverpool’s 1-0 win at Stoke in the first leg at the Britannia Stadium earlier this month.
Liverpool and Stoke failed to win the semi-final tie in normal tie and extra-time so the last-four clash went to penalties at Anfield.
Peter Crouch, Emre Can and Marc Muniesa missed their attempts before Allen converted the winning spot-kick to secure Liverpool’s place in the Wembley final on 28 February.
Unsurprisingly, the Liverpool players wasted no time taking to Instagram to revel in their semi-final win.
MORE: Man United latest news
MORE: Arsenal latest news
MORE: Chelsea latest news
MORE: Liverpool latest news