The bout was one of the scheduled highlights of the Mayweather-McGregor undercard at the T-Mobile Arena.
Jack, who improved to 22-1-3 with the win, dominated British star Cleverly from start to finish to score a technical knockout after 2min 47sec of the fifth round.
The bout was one of the scheduled highlights of the Floyd Mayweather-Conor McGregor undercard at the T-Mobile Arena.
Cleverly, defending his title for the first time, was struggling from the opening bell, with Jack's piercing jab and right hand finding their target repeatedly.
Cleverly looked to be finding his range with a flurry of punches at the end of the first, connecting with a right to the chin.
But it was a fleeting rally with Jack firmly back in control thereafter.
A dominant fourth round display saw the 33-year-old rock Cleverly with a thunderous left hook to extend his lead.
The fifth round was almost entirely one-way traffic, Jack connecting with a stream of jabs and hooks to force Cleverly onto the ropes.
With Jack jolting Cleverly at will, referee Tony Weeks had seen enough, halting the fight to protect the champion from further punishment.