John Cena Loses To Austin Theory At WrestleMania 39

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 into 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.

Naturally, with Cena being a WWE icon, Theory was met with boos whenever he gained an edge in the match.

Cena and Theory both had opportunities to end the bout early ... but both were able to escape each pin attempt.

Cena ended up tapping out Theory with an STF ... but the referee did not see it, as he was dealing with his own problems.

Ultimately, Theory took down his hero with his second chance and kept his title in the process.

Of course, the match meant so much for Theory ... who told us earlier this week he idolized Cena growing up ... but made sure to point out he has no intention of being a copycat.