Vanquished Thabiso "The Rock" Mchunu says there are titles he must win before he can bring his boxing career to an end.

He was reacting to his failed bid to wrest the WBO cruiserweight belt from Ukrainian Oleksandr Usyk in the USA on December 17.

Veteran American referee Lou Moret waved the fight off at 1:53 of the ninth round after Mchunu had gone down for the third time.

Usyk improved his knockout ratio to 11 from as many bouts. Mchunu has three losses.

When Usyk won the belt in September in his 10th fight, he actually broke the cruiserweight division record for winning a world title with the fewest fights, surpassing legend Evander Holyfield.

Said Mchunu: "I am still in the fight game big time. I intend to quit at 35 which means I still have seven more years to run races and win titles. Usyk has improved a lot. No excuses, he got the better of me."

Mchunu's corner was manned by Sean and George Smith as well as Shannon Strydom. Mchunu scored with counter left hands in this all-southpaw battle.

"I won rounds one, two, three and eight until he got the better of me in nine. I fought my best fight, intending to win. He landed many punches and was able to use his height. I learned a lot from this fight. I doubt that there is a cruiserweight today who can beat Usyk," said Mchunu.

Usyk landed the more accurate punches, dropping Mchunu down with a left uppercut in the sixth round. Mchunu was down again in round nine after a flurry of punches before Usyk scored the final knockdown later in the round with a left hook. The fight was a curtain raiser to the WBC international light heavyweight contest between holder Joe Smith Junior who knocked out former multiple world champion at middleweight and light heavyweight Bernard Hopkins through the ropes in round eight, effectively ending the 51-year-old's 28-year boxing career.