World Player of the Year Lionel Messi scored a hat-trick for Barca, taking his tally for the season to 13, while substitute Bojan Krkic scored twice, Andres Iniesta and Pedro bagged one apiece and Santiago Acasiete netted an own goal.
Barcelona's biggest away win since they hammered Las Palmas by the same scoreline in 1959 led to struggling Almeria sacking their coach Juan Manuel Lillo soon after the match.
At the Bernabeu, La Liga top scorer Cristiano Ronaldo also bagged a hat-trick to move on to 14 goals, while Gonzalo Higuain and Sergio Ramos also netted to ensure Jose Mourinho's side maintained their one-point advantage at the top.
Villarreal's Italy striker Giuseppe Rossi equalised in the 73rd minute to cancel out Aritz Aduriz's 21st-minute opener.
David Villa's backheel amidst a crowd of defenders completed a neat one-two with Messi, and the Argentine fired past Diego Alves from the edge of the area in the 17th minute.
Almost immediately, Iniesta made it 2-0 by pouncing to score as a defender deflected a pass in the area with his leg and in the 27th similar panic led to Acasiete steering Maxwell's cross into his own net.
Fontas demonstrated his class with a majestic long pass out of defence for Pedro to scamper clear and score in the 35th and two minutes later Messi burst into the area on to Pedro's pass and scored at the second attempt.
Bojan picked up Messi's through pass and made it 6-0 after squirming between three defenders in the 62nd, and Messi completed his hat-trick after Alves could only parry Villa's long-range shot.
"It wasn't a normal game. I don't know if it was because we did well or they did badly but we made the most of our chances," Bojan told Spanish television.
"They are three important points and the 'clasico' is only another three points, but it's true the result helps us to keep moving forward."
