The two teams clash in Manaus on very different levels of morale, with the U.S. still buzzing after John Brooks' headed winner against Ghana gave Jurgen Klinsmann's charges the belief to believe they can make it into the next round.
In contrast, Portugal are combatting rumours about the injury status of talisman Cristiano Ronaldo and are smarting after a thrashing at the hands of Germany in the opening game, as well as a burgeoning injury crisis, with Fabio Coentrao already ruled out for the whole tournament.
It should still be an even game, but with much of the pre-match buildup set to focus on Ronaldo, the Real Madrid forward could be a decisive influence in how things pan out. Without their captain, Portugal will be even more vulnerable than against Germany and the U.S. could claim with their game against Germany to spare, potentially setting up a mouthwatering clash with Russia in the next round.
Match Date/Time: 23rd June, 6 p.m. ET
Venue: Arena Amazonia, Manaus
TV: ESPN (U.S. English), ESPN Deportes (U.S. Spanish), BBC One (U.K.), CBC (Canada), RTP1 (Portugal)
U.S. Announcers: Ian Darke, Taylor Twellman
Online: ESPN3 (U.S.), BBC iPlayer (U.K.), CBC Live Streaming (Canada)