Two minutes later it was 2-0 to the visitors as Messi again played provider, this time slotting Cristian Tello in down the left to find the bottom corner.
In the 13th minute Messi grabbed a goal himself and it was another good finish, this time set up by Sergi Roberto.
Barca continued to dominate and could have been further ahead, and they did get their fourth just before the break through Jonathan Dos Santos.
Within 10 minutes of the restart the Blaugrana had added another two, both from Dongou. First he latched onto a threaded pass from Sanchez to slot into the net, before more great work from the winger found the 18-year-old again for an even simpler finish.
The scoring was finally complete in the 87th minute by youngster Joan Angel Roman, who weaved into the box and delayed his shot until the perfect moment to roll it home.