Perhaps the most consistent and everpresent figure of the decade, DaMarcus Beasley, is an easy selection at left-back. Breaking onto the scene in 2013, he captained the USMNT to Gold Cup success later that year before performing superbly in the 2014 World Cup. He also became the first American to play in five World Cup cycles, partaking in three in this decade alone.
Opposite of Beasley, I have plumped for Steve Cherundolo. He may have only featured for the USMNT until 2012, but such is the desperate nature of the other options, it is Cherundolo or bust. Plus, while his best years came before 2010, the best full-back the USMNT has ever produced was excellent in his final two years.
He played every minute of the 2010 World Cup, every minute on the way to the Gold Cup final a year later, only missing out on the latter 79 minutes of the final due to injruy. It seems odd to give a place to a player who played only a fifth of the decade, but who else would you have?