Celta Vigo are up into fifth after beating Real Zaragoza, while there were also wins for Atletico Madrid and Real Sociedad.
It was one-way traffic at Estadio Balaidos with the home side running riot after half-time.
Nestor Cannobio opened the scoring from close range on 30 minutes after Cesar disposed Fernando Baiano when through on goal.
The home side doubled their advantage seconds after the interval when Jorge fired home with Cesar well out of his goal.
Celta turned on the style late on with Jesus Perera adding a third within minutes of entering the fray as a substitute.
Less than a minute later and it was four when Cannobio added his second of the game with a fine chip over Cesar.
Real Sociedad's improving form continued with a 2-0 win over an under-strength Villarreal at El Madrigal.
The contest was all over in the opening half hour with goals from Mikel Alonso and Mark Gonzalez putting the visitors in control.
Villarreal clearly had one eye on next weekend's UEFA Champions League semi-final second leg clash with coach Manuel Pellegrini resting several key stars.
Alaves' season is going from bad to worse following a 1-0 home defeat to Atletico Madrid.
Antonio Lopez's goal after just 22 minutes means Alaves now sit in the bottom three in La Liga.