All four goals were in the opening half-hour as the unbeaten leaders overcame their city rivals for their 17th victory in 18 games this season.
They are 11 points clear of Atletico Madrid - who were held to a 1-1 draw by Mallorca - and 16 ahead of hated rivals Real Madrid, who beat Real Sociedad in a thriller at the Bernabeu.
Andres Iniesta crossed low for Xavi to sidefoot home the opener after 10 minutes and Pedro netted his first from a Cesc Fabregas pull back in the 15th.
Pedro scampered away on to a Sergio Busquets through ball in the 27th and dinked his shot over Francisco Casilla for the third and Fabregas went down for a penalty two minutes later.
World Player of the Year Lionel Messi, who netted 91 goals for club and country in 2012, scored from the spot to rack up his 27th in the league this season.
The Argentine forward was later denied by the woodwork from a free-kick.