Valencia moved two points lead at Real Sociedad before the Basque club host Granada on Monday.
Soldado slotted a penalty in the 28th minute after Jordi Figueras Dani Parejo was fouled in the area.
He added a second goal on 34 to take his season tally to 21 league goals, and Andres Guardado sealed the victory with 62.
Barcelona clinched the league title Saturday after Real Madrid drew 1-1 in Spanish.
Barcelona, Madrid, and Atletico Madrid have already locked up the other three Champions League berths.