Gervonta Davis knocked out Frank Martin to retain his World Boxing Association lightweight crown in Las Vegas on Saturday.

Davis used his physicality to dominate the unbeaten Martin before unloading against the challenger in the eighth round.

After backing Martin onto the ropes with a flurry of punches, Davis connected with a devastating left hook that sent the challenger crashing to the canvas at the MGM Grand Garden Arena.

Davis improved to 30-0, with 28 knockouts following the win against Martin, the 29-year-old from Detroit who had been unbeaten in 18 fights before Saturday's defeat.