Spain defender Sergio Ramos has talked up the importance of topping Group B after grinding out a 1-0 win against Iran at the Kazan Arena.

La Roja were made to work hard for their first three-point haul at the 2018 World Cup, scoring the only goal of the game 54 minutes in through Diego Costa.

Ramos has suggested that Iran made life tough for his side by repeatedly wasting time when the game was level at 0-0, but admits that an improved performance is required against Morocco to land top spot ahead of Portugal.

"They went out to waste time, whereas we like to win in a different way," he told reporters. "We leave happy. We've taken another step forward and now we have to try to top our group, it's our objective. I still think we can improve in all aspects."

Portugal and Spain are level on points and goal difference heading into the final round of fixtures.