Barca have 60 points from 23 matches while Valencia climbed to third on 38 after a 1-1 home draw with Malaga, who moved above Atletico Madrid into sixth spot.
Sevilla, in fourth, visit Espanyol on Sunday on a run of three straight defeats and Atletico host city rivals Getafe.
Defender Melli beat Sergio Busquets to a corner and sent a looping header past goalkeeper Victor Valdes. A defensive lapse then let Mark Gonzalez in to double the home side's lead.
Sergio Garcia's cross from the right was allowed through to the Chilean forward and he volleyed low across Valdes into the bottom corner.
Ricardo Pereira blocked the first effort by Eto'o but the Cameroon striker drove home the rebound.
With the visitors pushing forward, Ricardo Oliveira had a chance to make it 3-1 when he went clean through but Valdes blocked the Brazilian's weak effort.
Eto'o grabbed his second double in consecutive weeks with a smart finish through the legs of Fernando Vega with six minutes left, the 23rd goal of the season for the league's top scorer.
"We were pushing for the win and I have no reason to reproach my players," Guardiola told reporters. "It was a good performance against a very good team."
David Villa put Valencia in front against Malaga with a clinical finish just after the break, the Spain striker picking up David Silva's pass and curling a shot over keeper Inaki Goitia.
