Well, the Mexicans were not that bad at the FIFA Conderations Cup in Germany in June. All the participating teams included their top stars so actually Mexico beat the best team that World Champions Brazil could offer.
Japan - Mexico 1 - 3
Mexico - Brazil 1 - 0
Greece - Mexico 0 - 0
Semi-final:
Argentina - Mexico 1 - 1 after extra time, ARG won 6 - 5 on penalties and went on to win the touirnament against BRA.
I really think the US team is at least semi-final material next year if they play enough challenging test matches. To beat Mexico in a decisive qualifier is not an easy task for any team in the World.