Oleksandr Usyk beat Tyson Fury by split decision to win the world's first undisputed heavyweight championship on Sunday, an unprecedented feat in boxing's four-belt era.

Britain's Fury was the early aggressor but Usyk gradually took charge and the "Gypsy King" was saved by the bell in the ninth round before slumping to his first career defeat.

Ukraine's Usyk joins the likes of Muhammad Ali, Joe Louis and Mike Tyson as undisputed heavyweight champion, the first since boxing recognised four major belts in the 2000s.

With the win, the still-undefeated former undisputed cruiserweight champion can legitimately claim to be the best of this era, although a rematch expected in October could provide another twist.

"It is a big opportunity for me, for my family, for my country," said Usyk, 37, who briefly served as a soldier after Russia launched its military campaign in Ukraine in 2022.

"It's a great time, a great day," he said, adding that he was "ready for a rematch".

Fury called it a "fantastic fight with Oleksandr".

"I believe I won that fight, I believe he won a few of the rounds, but I won the majority of them," he said.

"You know his country is at war, so people are siding with the country at war but make no mistake, I won that fight in my opinion and I will be back."

Britain's Lennox Lewis was the last man to unify the heavyweight belts -- three at the time -- after beating Evander Holyfield in 1999.

Two judges scored it for Usyk by scores of 115-112 and 114-113 while the third gave it to Fury 114-113. The victory extended Usyk's professional record to 22-0. After his first loss, Fury stands at 34-1-1.

Usyk, who adds Fury's WBC belt to his IBF, WBA and WBO titles, looks set to go down as one of the greats after dominating at amateur, cruiserweight and now the top division.

A fired-up Fury came running out of his corner to start the fight and the 2.06 metre boxer was quickly into his rhythm, keeping the shorter Usyk back with his jab and playing to the crowd.

Usyk got inside with some quick combinations while Fury landed some heavy body shots. By round four, the Mancunian was taunting his ever-advancing opponent and showboating, guard down.

Usyk called two low shots in round five and got caught with a left hook as Fury continued to look comfortable, landing a telling uppercut in the following round and bobbing and weaving to stay out of range.

But the Ukrainian tagged Fury with two clean lefts in the seventh and landed a punishing hook that dazed the "Gypsy King" in the eighth.

By the next round, a relentless Usyk barrage had Fury in serious trouble and the wobbling, bleeding Mancunian took a standing count before being saved by the bell.

Fury recovered his poise and with the match in the balance heading into the final round, both fighters were finding the target.

Wladimir Klitschko was among the legends watching along with Saudi-based football stars Cristiano Ronaldo and Neymar, who like boxing are grateful beneficiaries of the oil-rich monarchy's lavish push into sports. (AFP)