Alaves crumbled after two goals in two minutes gave Real a commanding position mid-way through the first-half.
Raul opened the scoring after 21 minutes, before Guti struck to double the lead.
Spain's all-time leading goalscorer Fernando Hierro grabbed a third shortly after the break, with Raul grabbing a second and Helguera also getting onto the scoresheet to complete the demolition job.
The title has been wrapped up because, despite having three games left to play and a nine point deficit, Depor have an inferior head-to-head record against Real.
In the other Primera Liga game of the night Celta Vigo recorded a 1-0 victory over Las Palmas and all but secured a place in next season's Uefa cup.
The deciding goal was scored by Argentinian international Eduardo Berizzo in the 50th minute and Las Palmas could find no reply in the remaining 40 minutes.
