Dominic Breazeale traded knockdowns with Izu Ugonoh in one of the best heavyweight battles of the year so far.
The pair felt each other out in the first two rounds until the contest exploded early in the third as Ugonoh hit the canvas. Breazeale looked on the verge of being put down himself but managed to catch Ugonoh coming in and drop him to the floor.
Ugonoh came back strong towards the end of the round by landing two solid rights before putting Breazeale down in the fourth as the tide turned in his favor.
Following a telling off from his corner, Breazeale came out fast in the fifth and managed to score another knockdown before finishing the fight by putting Ugonoh through the ropes after he managed to get to his feet against the odds.
The win means Breazeale is back in the win column following his loss to Anthony Joshua in 2016, although on this evidence the American will need to work more on his defense.
In other results, Former 200 pound contender Iago Kiladze made a successful heavyweight debut by knocking out Byron Polley in the first round.
Cruiserweight prospect Deon Nicholson took just 40 seconds to stop Josh Rasberry before top division puncher Junior Fa also remained undefeated by halting Keith Barr in the third.
Earlier, heavyweight Robert Alfonso defeated Keith Thompson via first round knockout, whilst at middleweight Thomas Knox out-pointed Anthony Retic over four.