Barça's Allegri precedent: a 4-0 turnaround in Camp Nou
The Liga side found themselves 2-0 down after the first leg in the San Siro in the 2012-13 Champions League but went through after a thrilling comeback.
March 12, 2013. Barcelona are two goals down against Massimiliano Allegri's AC Milan side after the first leg in San Siro.
Needing to mount a comeback to reach the quarterfinals, goals from Leo Messi (2), David Villa and Jordi Alba saw off the Serie A giants.
On Wednesday night Barça will have to it all again against Allegri's Juventus, who carry a 3-0 advantage into the game after the opening fixture.