New Zealand lock Sonny Bill Williams has become a boxing champion following a first-round victory over Clarence Tillman.

Williams, who featured during New Zealand's World Cup success last year, knocked out veteran Tillman with a second of round one remaining.

The victory has seen the 26-year-old secure the vacant New Zealand heavyweight title.

Williams has taken up boxing on a part-time basis before he starts playing in the 2012 Super Rugby with Waikato Chiefs.