WWE Superstar Austin Theory just shocked the crowd and defeated the legendary John Cena to kick off WrestleMania 39 ... with the United States Champion retaining his belt to beat his childhood idol.
The entire match was insane from start to finish ... with Cena and Theory showing their strengths throughout.
Cena hit Theory with a quick couple of clotheslines in the beginning ... which threw Theory for a tizzy for a bit. Austin quickly regained his composure, and he took over the match for the next several minutes.
It was as back-and-forth as it could get moving forward -- with both Theory and Cena trading insanely hard hits.