Two first-half penalties, from captain Andres Iniesta and Cesc Fabregas, set the champions on their way and Alexis Sanchez put the result beyond doubt 19 minutes from time - soon after the visitors had lost midfielder Manuel Iturra to a red card.
Pedro added a fourth in the final minute to complete the rout as Barca moved provisionally six points clear at the summit ahead of the rest of the weekend's action.
Afterwards, defender Marc Bartra said: "We were really good, we were in control throughout.
"Tata told us despite the players out, we had to push on."
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