HAMBURG — Wladimir Klitschko knocked out the previously unbeaten Kubrat Pulev in the fifth round to retain his four heavyweight belts on Saturday. Klitschko sent the Bulgarian flying back with a huge left punch to his jaw, leaving him sprawled on the canvas and giving referee Tony Weeks no option but to end the bout.

Klitschko, taller with a longer reach, dominated from the start and had the IBF’s mandatory challenger down twice in the opening round. Klitschko dropped him to the canvas again in the third, which Pulev did well to finish with a bloody left eye. Just when the challenger seemed to be improving, Klitschko finished the bout abruptly, 2 minutes, 11 seconds into the fifth.

Klitschko recorded his 54th knockout in 63 wins, with three defeats, and he dedicated his latest victory to the Ukrainian people, “who are going through tough times.”

Pulev, who dropped to 20-1 (11 KOs), said Klitschko was “lucky” and used dirty tricks during the contest.

“Wladimir is a really good opponent, but he was lucky. I want a rematch. I’ll win the next time,” Pulev said. “There’s luck in boxing. He’s a good boxer but he’s unsportsmanlike. There were a lot of tricks.”

Pulev also took plenty of shots at the champion prior to the fight, but he was made to pay for his pre-fight statements when he described Klitschko as behaving "like a girl" and saying he "has no heart".

"I have never seen such arrogance from an opponent and there was a price to pay for that," said Klitschko. "I don't think he realized he was playing in the champions league."

After the fight, Klitschko flew to Nashville in the early hours of the morning to be with his girlfriend, TV actress Hayden Panettiere, who is expecting their first baby next month.

"The baby is almost there, I hope I don't miss it, because I really want to experience my own child being born," said the proud father-to-be.

Klitschko does not want to take a long break from boxing after the birth. He is closing in on legendary Joe Louis' record of 25 heavyweight title defences.