Spain defender Gerard Pique said it was important for their team to show that the sacking of their former head coach Julen Lopetegui has not had any lingering effects on the squad.
Lopetegui was replaced by Spain's sporting director Fernando Hierro after agreeing to take charge of managerless Real Madrid after the World Cup without notifying the Royal Spanish Football Federation that he was in talks with the club.
Spain and Portugal played out an epic 3-3 draw at Sochi's Fisht Stadium on Saturday morning (AEST) with Portugal forward Cristiano Ronaldo scoring a hat-trick.
Diego Costa recorded a brace for Spain, while Nacho also scored with an early contender for goal of the tournament.
"The win was important but the main thing was to show everyone that we can play well following (Julen) Lopetegui's departure," Pique said.
The game was difficult but we played as a team and scored three goals. It is important not to lose concentration now... But the draw didn't suit either us or Portugal.
Spain and Portugal were both drawn in Group B alongside Morocco and Iran.
The 2018 FIFA World Cup will last till July 15, with the games set to be played at 12 stadiums across 11 Russian cities.