The hosts are the lowest-ranked side at the World Cup and entered the competition on the back of a seven-match winless streak.
But on the opening day, 14 June, they thrashed Saudi Arabia 5-0 and followed that up five days later with a 3-1 victory over Egypt.
Denis Cheryshev scored three times in those two games to be among the leading scorers at the World Cup.
The 27-year-old plies his weekly trade at Villareal in La Liga and has first-hand knowledge of the skills of a side containing World Cup and Champions League winners such as Sergio Ramos, Andres Iniesta and Gerard Piqué.
Despite the apparent gulf in class and experience, Cheryshev says he and his teammates need to maintain their confidence.
“We can always win and that's what we need to believe,” he said. “We just need to think about victory.”
Russia go into the clash on the back of a 3-0 defeat against Uruguay in their final Group A match in Samara on 25 June.
That they are in the last 16 is a surprise and, after world champions Germany departed with only one win in three games, Spain's seasoned campaigners say they are taking nothing for granted.
David Silva who was in the 2010 World Cup winning squad said his side would take the match seriously. “We will treat it as if we were playing against Brazil,” he added.
The omens are unfavourable for the Spaniards. They have never beaten a host nation in eight attempts. Spain coach Fernando Hierro was in the Spain team when unfancied South Korea knocked them out on penalties in 2002.
"Statistics are made to be broken," Hierro said. "Why are we always looking backwards? We've had three games here but we're going to look at what happened 10 or 15 years ago? No, it's about what happens on Sunday afternoon"