'Filthy': Nikita Tszyu knocks out Oscar Diaz but not without late controversy in dominant display

Nikita Tszyu has knocked out Oscar Diaz in Newcastle, dominating proceedings despite a controversial finish.

The TKO came in the sixth round after Diaz dropped to a knee following some heavy hits.

Tszyu delivered two quick punches in the moments following the knee touching the mat, leading to the Spaniard's corner exploding in fury.

READ MORE: Mundine's son jabs booing crowd after contentious win

READ MORE: FA urges Fed Square to overturn 'absurd' World Cup ban

READ MORE: 'He had a point': Gus lifts lid on Bracey v Gallen TV showdown

"They're unhappy with those punches, the corner," commentator Ben Damon told Kayo.

The referee got to a nine-count before Diaz got back to his feet and managed to survive the remainder of the round as Tszyu teed off.

However, the fight was then called off between rounds, with the Spanish fighter unable to continue.

The Aussie was apologetic after the late punches, saying after the fight he didn't notice the knee hitting the mat.

"I mean, it was just a split-second reaction. I didn't see that his knee was on the ground. I saw him bent over. In my experience, if they're bent over then keep punching," Tszyu said.

Despite the controversial finish, the fight was all Tszyu, who dominated from start to finish, throwing and landing double the punches of his opponent.

He dropped Diaz in the second round and rocked him again in the fourth before the eventual finish in the sixth.

Boxing commentator Peter Badel was incredibly impressed with the performance.

"The way it ended was a bit controversial. I know they were a bit filthy the Spanish camp," Badel said.

"Nikita was clearly on top and he apologised for hitting him late while he was down.

"Split-second moments. It all happens so quick, but at the end of the day, probably not ideal. Nikita was apologetic.

"Overall, an emphatic and comprehensive performance."

Badel believes the fight proves Tszyu belongs on the international stage.

"For the first time, I now believe Nikita can be the whole package. I never thought he would be the fighter that he is," he said.

"He was always the butcher, but tonight he was a brutal practitioner.

"That was outstanding. On this performance, Nikita has graduated from domestic slugger to international contender. He is the real deal."

Tszyu said he's "not really thinking about world titles" but was happy to have a solid six-round bout after a few quick finishes.

"Good to get the rounds in. Good to feel the energy of the crowd. Good to get a sweat up. Good to work for my money," he said.

"He's really tough. I landed some really solid shots on his forehead and I'm surprised he was able to take some of them. We had to start working the body and we got there in the end.

"I'm not really there yet with confidence. I still consider myself a novice and I think I have a lot more to learn before I go for the world titles. They'll come with discipline and consistency and hard work, growth is inevitable."

Fellow Aussie boxer Liam Paro was also impressed with what he saw from Tszyu.

"That's a huge win. That proves he's at the world level taking out a top 15 world contender," Paro said.

"In saying that Diaz was a tough customer. That was a fight Nikita needed to build. He's a few fights away from a world title I reckon.

"He was a lot more composed and a lot more balanced. It was what we needed to see."

With the win, Tszyu takes home the vacant WBO International Super Welterweight Title.