Tello hat-trick puts Barca on brink of Cup semis
Barcelona's forward Cristian Tello (2nd R) celebrates his third goal with Argentinian forward Lionel Messi (R) and goalkeeper Victor Valdes (L) at the Ciutat de Valencia stadium in Valencia on January 22, 2014 - by Jose Jordan
Nabil El Zhar had fired the hosts into a shock lead midway through the first-half.
However, after an unfortunate Juanfran own goal had levelled matters just after half-time, Tello then sped onto Messi's through ball to fire home on the hour mark.
The two combined once more 10 minutes from time and another lovely Messi pass allowed the 22-year-old to volley home his hat-trick five minutes later to leave the second-leg at the Camp Nou next Wednesday a formality.
Barca boss Gerardo Martino had made eight changes to the side that could only manage a 1-1 draw with Levante in La Liga on Sunday with Pedro Rodriguez and Xavi joining Messi as the only three players to retain their place.
And Pedro nearly repaid Martino's faith immediately as he struck the base of the post after only five minutes.
However, just as at the weekend, it was Levante who took the lead from a set-piece as El Zhar prodded home from close range after Jose Manuel Pinto had parried his first effort.
Barca were handed a huge slice of luck to equalise eight minutes after half-time when Loukas Vyntra fired the ball off teammate Juanfran and the ball rebounded past the helpless Javi Jimenez into the net.
Thereafter, though, it was a procession as Tello thundered home his first moments later from Messi's first assist.
The winger then curled home his second of the evening after the defence had again been attracted towards Messi.
And Tello sealed a memorable evening five minutes later with a another thumping finish from Messi's clipped ball over the top.
Barca will most likely face Real Sociedad in the last four after they beat third-tier side Racing Santander 3-1 at home in their quarter-final, first-leg.