Logan Paul knew he was in for the fight of his life against Roman Reigns at Crown Jewel ... and even though he got an assist from his brother, Jake, he couldn't come away with the championship.

Logan proved once again he belonged in the ring on Saturday ... showing off his remarkable athleticism against the undisputed WWE Universal Champion in an incredibly entertaining fight.

Logan paid homage to WWE legend Eddie Guerrero -- as he did in his WrestleMania 38 match -- by hitting Reigns with a frog splash off the top rope through the announcer's table.

The craziest part ... he did it with a phone in his hand, recording the entire stunt -- talk about insane!!

Logan also showed Shawn Michaels some appreciation ... when he attempted to hit the WWE champ with The Heartbreak Kid's signature sweet chin music finisher -- though he was unsuccessful.

As we previously teased ... the "Problem Child" was in Saudi Arabia to watch his brother ahead of the biggest match of his life -- but also to look out for Logan in case he ran into any trouble against Reigns.

Well, that moment arose when the Usos -- a part of "The Bloodline" group with Roman -- started attacking Logan's entourage, who had been sitting ringside.

Jimmy and Jey Uso then started beating up Logan's buddies in the ring ... when suddenly, Jake hit the stage and walked down to the ring to confront the Usos while his "It's Everyday Bro" song blared through the speakers.

The undefeated 6-0 boxer got into the ring without hesitation and even dropped one of the undisputed tag team champs!!

Logan's performance had social media buzzin' ... his former boxing nemesis and Internet celebrity KSI was thoroughly pleased with the spectacle, tweeting, "What a match, bro."