Tenshin Nasukawa has revealed he underestimated Floyd Mayweather Jr prior to his first round knockout loss at the hands of the unbeaten American on New Year's Eve.

The 20-year-old Japanese kickboxer, who stands just 5ft 4inches off the ground, was thrust into the global spotlight after knockout victories over former IBF world champion Amnat Ruenroeng and former Muay Thai world champion Wanchalong PK Senchaigym.

In November last year, Nasukawa was then offered the opportunity of a lifetime - to fight boxing immortal Floyd Mayweather Jr at Rizin 14 in Japan.

Mayweather arrived 90 minutes late to the Saitama Arena on fight night, although it appeared not to affect his performance as the 41-year-old punished Nasukawa from the opening bell.

‘Money’ dropped the younger fighter three times in the opening round when Nasukawa’s corner had seen enough and threw the white towel of surrender after just 139 seconds.

The former pound-for-pound king earned a staggering $3.25m per minute for his cameo appearance and admitted after the clash that he hadn’t even trained for the bout.

The loss was devastating for Nasukawa and his team, but the Tokyo-born fighter insists he has “no regrets” after sharing the ring with one of the greatest boxers to ever walk the earth and referred to the event as “the opportunity of a lifetime.”

“I have worked hard with a big dream in the combat world. Karate, Kickboxing, MMA and Boxing,” said Nasukawa, per World Boxing News.

“When I first got the offer I took it in a flash. I thought this was an opportunity of a lifetime, and although there were significant differences in accomplishments and weight classes, I felt that I must not run and take on the challenge.

“The days since the fight was confirmed have been enjoyable but with concerns, and I spent the time thinking about many things.

“At the end of the day, I got finished, but I have no regrets. I am disappointed at myself since I thought I could have done better. But I will face the facts and will continue to take on any challenge.”

He added: “I learned that I didn’t work hard enough to earn this opportunity. I will use this defeat to improve myself and move forward this year.

“Despite all the things that happened leading up to the fight, I came to realise how truly great Mayweather was. I was the one underestimating him.

“I promise to make it to that level. It may take some time for me to become the man to haul the industry on my shoulders, but please continue to support.

“Everybody who worked to make this fight happen, thank you very much. Mr. Mayweather, thank you very much.”

It is unclear when Nasukawa will next compete, but after five kickboxing wins in 2018, many believe the 20-year-old will return to what he knows best and build on his undefeated record.