#4 Kevin Owens
John Cena did his best to restore the prestige of the United States Championship, the first singles championship he had won in WWE. Cena defended his U.S. title in an open challenge against multiple opponents.
One such opponent was the then NXT Champion, Kevin Owens. While KO didn't actually face Cena for the title, the altercation led to a champion vs champion match at the Elimination Chamber PPV.
At the PPV, Owens shocked the world by defeating the Cenation Leader clean. This victory came at a point when NXT wasn't as big as it is now. The win was a huge boost not just for Kevin Owens but also for NXT, which was merely considered as a development system at that time.
While Cena did go on to win the feud between the two, a win over a multiple time world champion made Kevin Owens a force to be reckoned with.