Murat Gassiev added the WBA belt to his IBF world cruiserweight title by stopping Yunier Dorticos to reach the World Boxing Super Series final.
Russian Gassiev, undefeated in 26 bouts, was more offensive and broke the Cuban's resistance with three knockdowns in the final round.
A savage left hook delivered the first before Gassiev, 24, closed out in Sochi, Russia.
He faces WBO and WBC champion Oleksandr Usyk in the final on 11 May.
Ukraine's Usyk was ringside to watch Gassiev knock 31-year-old Dorticos through the ropes in the final round at the Bolshoy Ice Dome, and both finalists faced off in the ring after the fight.
The champion will become the first man in history to hold all four cruiserweight titles as they have each added to the world titles they held since the knockout tournament started in September.
In the super-middleweight division, Chris Eubank Jr and WBA super-middleweight champion and fellow Briton George Groves will contest a place in the final on 17 February.
Compatriot Callum Smith, faces Germany's Juergen Braehmer in the other semi-final.