SYDNEY (REUTERS) - Winger Ben Smith scored a hat-trick as a ruthless New Zealand opened their Rugby Championship title defence with a six-try, 47-29 victory over Australia on Saturday to ruin Ewen McKenzie's first match as Wallabies coach.

The world champions scored three tries either side of half-time at the Olympic Stadium with flyhalf Aaron Cruden, captain Richie McCaw and centre Conrad Smith supplementing Ben Smith's triple score.

Scrum-half Will Genia and James O'Connor scored what were ultimately consolation tries for the home side with Christian Leali'ifano remaining flawless in international rugby with seven kicks from seven attempts for 19 points with his boot.

As well as giving the All Blacks a bonus point in the Rugby Championship, the victory means Australia must win both the return in Wellington next week and a third Test in Dunedin in October to win back the Bledisloe Cup for the first time since 2003.