According to police records, Johnson had a warrant out for his arrest stemming from an incident in 2019 in which he allegedly used someone's credit card without their permission to purchase a flight.

Cops say Johnson illegally bought a round-trip ticket from Ft. Lauderdale, FL to Newark, NJ with the card.

So, when 37-year-old Johnson was in Connecticut on Friday for his fight at Mohegan Sun Arena against Jose Augusto -- cops nabbed him shortly after he scored the big knockout victory.

Records show New Canaan Police Dept officers put Johnson in custody at the arena and then transported him to headquarters for processing -- where he took a mug shot.

Johnson was booked on several charges, including identity theft, and was later released on $500 bond. He's due in court in June for a hearing in the case.

Rumble's fight against Augusto was his first pro bout since 2017 -- and it was an impressive win for him, considering the long layoff and the fact that he was knocked down in the 1st round.

Prior to the arrest, Johnson had been looking to become a big star in Bellator after a long and successful career with the UFC that included wins over guys like Alexander Gustafsson and Glover Teixeira.