But the Argentinian, making a milestone 400th appearance for the club, still more than played his part by laying on all of Barca's goals in this quarterfinal first leg tie.
Playing against opponents who held them in the Primera Division at the weekend, the Catalans trailed at the break to Nabil El Zhar's 31st-minute goal.
But Barca staged a second-half fightback, Juanfran turning Messi's pass into his own goal to bring them level in the 53rd minute.
And then Messi and Tello took centre stage, combining for three more goals in the 60th, 81st and 86th minutes.
In the other quarter-final first leg, Real Sociedad won 3-1 at home to Racing Santander.
A first-half brace from Mikel Gonzalez Martinez put the hosts in charge and they moved further clear as Carlos Vela added a third after an hour.
But Mamadou Kone gave the visitors hope going into the second leg with a goal in the 83rd minute.