The home side were ahead in the early stages of the second period when Xavi converted from close range, before Sanchez scored his second after 64 minutes.
Sanchez then turned provider after 70 minutes as he fed Neymar for their fourth of the match as Barcelona wrapped up the points in style.
Read how it all unfolded in Sports Mole's minute-by-minute live commentary of the action below.
BARCELONA: Valdes; Alves, Pique, Bartra, Adriano; Song, Xavi, Fabregas; Tello, Neymar, Sanchez
REAL VALLADOLID: Marino; Rueda, Rukavina, Valiente, Pena; Bergdich, Ebert, Baraja, Omar; Rossi, Guerra