All Blacks star and part-time boxer Sonny Bill Williams won the vacant New Zealand heavyweight title on Wednesday in style with a first-round knockout. The 26-year-old never looked under pressure as he rocked Clarence Tillman with a thundering left hook mid-way through the first round, following up with a flurry of blows before the referee ended the bout just before the bell. The easy win over Auckland-based American Tillman takes Williams' professional boxing record to five wins, three by knockout, against no losses. Tillman, 34, was supposed to represent a step up in opponent for Williams, whose most recent contest last June was a points win over an overweight 43-year-old. However, Tillman, a journeyman with an unspectacular record of 11 wins, eight losses and two draws failed to even land a blow on the dual rugby union and league international during their bout in Hamilton. Williams was originally supposed to fight fellow Kiwi Richard Tutaki but had to call in Tillman as a late replacement when Tutaki was arrested on drug-related charges. Tillman, carrying an extra 20 kilos (44 pounds) on Williams, faced questions about his fitness going into the fight. Williams, who has a special clause in his New Zealand Rugby Union contract allowing him to pursue his boxing career, will play for the Waikato Chiefs in this year's Super Rugby competition, beginning later this month.