With his left eye almost shut, the ringside doctor examined the fighter and declared the bout over but there was confusion and intrigue when they finally announced that Tso had retained his title.

Tso was expecting the worst as he slumped in his stool before the start of the seventh round.

Watch: Highlights of Rex Tso v Kohei Kono, his accidental headbutt and tearful speech

The unbeaten southpaw was forced yet again to come back from dire circumstances and it was heartbreaking to see the Hong Kong superstar struggle with his injury as he was clearly hampered.

But he did enough to win on points and seal victory yet again.

The Hong Kong boxer threw excellent combinations and kept the 36-year-old former two-time WBA champion at bay with his good counter-punching. But the pain must have been unbelievable.

“Sorry to my wife. I have hurt myself again. This time I really went for it. I followed my trainer’s advice. I have to thank my opponent Kono, He’s really so powerful. My head is really sore,” said a sobbing Tso, whose winning streak began in September 2011.

Tso was rushed to hospital – the first time as a professional – but he was well enough to speak to the delighted audience after his surprise victory.

“From the fourth round onwards I was super hurt but I had to continue,” he said. “Thanks Jake [trainer Vernano] and Ross Eathorne [conditioning and strength coach]. Thanks Jay Lau [his manager]. I did my very best!”

As boxing rules stipulates, if a clash of heads occurs during the first four rounds and if the doctor feels the bout must be stopped because a boxer cannot continue, they go to the scorecards. And Tso was leading the 12-round super flyweight contest on points against a highly aggressive and surprisingly game Kono. All three scorecards were an identical 68-66 in Tso’s favour.

Tso was first examined by the doctor in the sixth round. The referee momentarily stopped the fight to have the Hong Kong star looked at but with an assuring nod of head from the doctor, the fight went on to the roars of the 8,000 capacity crowd.

But his injury deteriorated with his left eye swollen to the point that he couldn’t see. And that’s when the referee asked for his eye to be examined again as the crowd hushed in silence, not sure what was happening. But as it turned out, it was all in Tso’s favour and he managed to retain his title and keep his unblemished record intact.

Promoter Lau said if the fight had been stopped within the first four rounds, it would have been a no-contest.

“The second round was an accidental headbutt. You could see that Rex’s head was completely swollen. The referee decided to carry on at first. He realised his left eye was completely shut. He couldn’t even see from that eye,” said Lau.

“After the referee and the doctor had a discussion, they decided to stop the fight then and there because they were worried that there may have been a fracture in his eye [socket]. Rex is going straight to the hospital. Don’t worry he can walk, stand and smile,” he said.

In the night’s other bouts, Japan’s Takuya Watanabe became the new WBO Oriental super featherweight champion after rallying to defeat China’s Leshan Li.

Watanabe, who was Tso’s sparring partner for the past two months in Hong Kong, landed a series of unanswered blows against a helpless Li, who had moments earlier hit the canvas after a devastating right hook. Referee stopped the fight with Watanabe winning by fifth-round TKO after surviving an earlier knockdown himself in the third round.

In the other three featured bouts, Japan’s Ayumi Goto continued her unbeaten run to eight bouts after defeating India’s Kirti Vashists in the co-main event to become the new WBO female Asia Pacific super bantamweight champion. Goto, a full-time receptionist and part-time glamour model, won the fight by unanimous decision. Judges scored it 79-72, 77-74, 78-73.

Hong Kong’s Raymond Poon Kai-ching won his light flyweight bout against Indonesia’s Frengky Rohi.

Poon, who is trying to follow in the same footsteps as Tso, improves his record to 4-1, 2 KOs after winning on the scorecard cards for a unanimous decision. Rohi suffered his first defeat as a professional and is now 5-1-1, 1 KO.