كتب : Hatem Maher
Barcelona are in charge of the league table with 49 points, two ahead of second-placed Sevilla who were held to a goalless away draw by Getafe.
Valencia, who also slipped up having drawn with bottom side Gimnastic 1-1, are third on 43 points ahead of Real Madrid with goal difference.
Barcelona were ahead in the 23rd minute when Bilbao defender Fernando Armorebieta converted Ludovic Giuly's low cross into his own net.
Spanish international midfielder Xavi Hernandez doubled the lead six minutes later following a brilliant team-work play.
After a series of passes, Ronaldinho's long ball found Eto'o inside the area before the Cameroonian sublimely laid off the ball to the onrushing Xavi, whose volley went into the back of the net.
Eto'o ensured the victory five minutes before the interval when he latched on to Ronaldinho's through pass before slotting the ball past Bilbao keeper Daniel Aranzubia.
Barcelona could have increased the score line on several occasions in the second-half after a superb show led by Brazilian playmaker Ronaldinho.
In the 59th minute, the former Paris Saint Germain produced the scene of the day when he side-stepped three defenders before firing a shot from a tight angle but Aranzubia tipped the ball into the bar.
The crossbar denied Ronaldinho's curling free-kick in the 77th minute.