What's on the line
Oh, nothing more than a spot in the quarterfinals and bragging rights among rivals as these two title hopefuls will fight to the death -- or until 90 minutes are up -- for Iberian supremacy. One, of course, will remain and face the winner of the other round of 16 game between Paraguay and Japan in the quarterfinals on July 3, giving the winner of this bout a very clear path to the semifinals, where the winner of Argentina-Germany will await.
Spain and Portugal are ranked second and third, respectively, in the world by FIFA. While the two have never met in a World Cup before, they have played 32 times, with Spain taking 15 wins and 12 games ending in a tie.
Style and tactics
It is as safe a bet as anything in soccer to say that Spain will try -- and probably succeed -- to dominate possession and trap Portugal in its own half, methodically picking apart Portugal's veteran defense with short, inch-perfect passing and clever through-balls for strikers David Villa and Fernando Torres to run onto.
Portugal, for its money, will play in its trusted 4-5-1 formation and try to exploit its biggest strength: its wingers. It will have a lot less of the ball than it is used to, though, and will have to adapt.
Players to watch
Fernando Torres, Spain. He hasn't been the Fernando Torres we know and admire as of yet in this tournament. His touch was conspicuously absent against Honduras, when he missed several chances he would never have failed to make materialize when in proper game-playing shape. Whether he was rushed back from injury or if his return merely coincides with a bad spell is hard to say. What's easy to say is that Spain will need him to match his striking partner, David Villa, in his sublime form in order to make good on expectations.
Cristiano Ronaldo, Portugal. The Real Madrid star has been dominant in just one game in this tournament. And even that one doesn't really count, as it came against a disconcertingly poor North Korean side. His game appears a little off, as he's resorted to launching long-range bombs, which always explode far from the goal, rather than take on opponents one-on-one and create both mayhem and space for teammates to capitalize on. Will he turn it around?
What we can expect
A fiery game between two teams who fancy their chances in this tournament and are both positioned better than they're likely to be in the foreseeable future to make a deep run. This should be one of the quicker games we've seen, as these are some of the fastest teams in the business.
A matchup to watch will be the one between Cristiano Ronaldo and Joan Capdevila. Capdevila, a left back, is Spain's only weakish link in the back, although he can be dangerous coming forward. If ever Ronaldo is to break out of this slump of sorts he is in -- because at his level, not dominating for a few games counts as a crisis of form -- he'll have to take profit from this mismatch.
At the other end, Spain will have to get Andres Iniesta involved regularly. He has missed a good chunk of this tournament due to injury and Spain's attacking engine has sometimes sputtered because of it. Integrating him regularly into the flow of the game will be paramount.
Spain will take this game, but not comfortably. Inevitably, the Spanish will outclass the Portuguese, whose defenders won't be able to keep up with the pace of the Spanish strikers (and Spain hasn't lost a game in which it has scored a goal in 39 games), and whose midfielders will wear themselves out chasing after pass-happy Spaniards. Look for this to be a chess match of sorts during the first half, and to break open in the second as the teams try to avoid extra time and begin to tire.
Leander Schaerlaeckens is a soccer writer for ESPN.com. He can be reached at firstname.lastname@example.org.