Chicago (AFP) - Russia's Artur Beterbiev knocked out British challenger Callum Johnson in the fourth round on Saturday to retain his International Boxing Federation light heavyweight world title.
Beterbiev, 33, maintained his perfect record with his 13th knockout win in 13 professional fights.
The 33-year-old Johnson, in his first world title fight, lost for the first time, falling to 17-1 but not before a game effort to topple the champion.
Beterbiev, who fights out of Canada, waded in early and dropped Johnson late in the first round.
The knockout artist was clearly looking to finish Johnson off in the second. He had landed a string of punishing blows when Johnson nailed him with a left hook that sent Beterbiev to the canvas at 1:24 of the second.
Beterbiev managed to stave off Johnson for the rest of the round, and the two traded more big blows in the third.
Beterbiev put Johnson down for the seocnd time with 37 seconds left in the fourth, landing two rights to the challenger's head.
Johnson tried to rise, but he couldn't beat referee Celestino Ruiz's count before it reached 10 and it was over at 2:36 of the fourth.
Johnson, who had fought just once in the past two years, admitted he was a bit "tense and nervous" coming in.
"Believe me, I'll be back, and I believe one day I'm going to be a world champion."
On the same card at Wintrust Arena, American Danny Roman retained his World Boxing Association super bantamweight world title with a 10th-round technical knockout of British challenger Gavin McDonnell.
Roman rocked McDonnell with a big right then pummelled him to the canvas before the bout was stopped at 2:36 of the 10th.
Roman improved to 26-2 with one drawn and 10 knockouts.
McDonnell fell to 20-2 with one drawn, again failing in a world title bid. His only prior defeat came in his only other world championship fight, when he dropped a majority decision to Rey Vargas last year in their duel for the vacant World Boxing Council super bantamweight world title.