By Brad Walter

Sonny Bill Williams versus Anthony Mundine. It is a fight many sports fans would love to see but only a select few were on hand as the pair went toe-to-toe for nine rounds in a New Zealand gym.

Mundine, the former NRL-star-turned-world-champion-boxer who paved the way for Williams and a growing number of athletes to try their hand at other sports, was in Hamilton earlier this month to help his close friend prepare for Saturday night's bout with 70-fight veteran Chauncy Welliver at Allphones Arena when the dual-code superstar's sparring partner failed to turn up.

Despite conceding a major height, weight and reach advantage to the  dual NRL premiership-winning forward and All Blacks star, Mundine agreed to fill the void and for the next 30 minutes they slugged it out. "We've both got too much manhood to hold back so I knew that even though he said he was going to take it easy he wouldn't," Mundine said.

"We started off doing three or four rounds and I was looking around wondering when he was going to stop because I hadn't done any sparring since my last fight [in November] but he wanted to keep going. We went to round five and then round six and he kept saying, 'Let's do another one'. We ended up doing nine rounds so the next day I was pretty sore and sorry but I am glad to have been able to give him the help he needed," Mundine said.

Asked who had won, Mundine said it would have been a draw as both landed significant blows on the other.  "I got him with a left hook and he said, 'You've rocked me, you've rocked me'," Mundine said. "But I turned southpaw one time and he threw a right hand and I put my head down but it hit me in the top of the head as I came up and I was dazed so he got me too."

Williams said it had been a good experience to spar with the lighter and faster Mundine, who quit the Dragons in 2000 to focus on boxing. "He had just finished 20 minutes of training on a heavy [punching] bag but I was still in the ring with a world champ and Choc's speed is a lot quicker than any heavyweight," said Williams. "It was good to do some work with him and be able to learn from the best. He got me with a left hook once, it was a beauty and buckled my legs."

Williams won't have to worry about speed when he steps into the ring against Welliver on Saturday night but is wary of the experience of an opponent who has sparred with the likes of Wladimir Klitschko, Mike Tyson, David Tua, Shane Cameron, Juan Carlos Gomez and Shannon Briggs and boasts 55 wins and five draws in a career that has taken the American all over the world to fight. In contrast, the bout will be just the seventh in Williams' career and his first since beating Francois Botha two years ago in Brisbane.

"I have a lot of respect for Chauncey, anyone who has stepped into the ring 70 times you have to respect, and that is the reason I have trained so hard," said Williams, who was ringside when Welliver lost a points decision to Kyotaro Fujimoto in Japan in 2012. Welliver said his main concern was Williams' athleticism.

"This guy is a better athlete than Michael Jordan, he can run he can jump he can do a little bit of everything," he said. "If you look at me, I am not the most athletic guy in the world but the one thing I am going to bring on Saturday night is heart and balls, and we are going to see if Sonny Bill can actually fight."