The All Blacks emerged triumphant in each of the past three years but South African rugby is on a high after the World Cup success and the 30-28 win at Carisbrook on Saturday night - the Springboks' first victory on New Zealand soil in a decade.
Australia are also likely to be more competitive under Kiwi coach Robbie Deans, meaning an inexperienced All Blacks squad face tough trips to Sydney, Brisbane and Cape Town as they try to win the title for a fourth successive year.
"It's going to be hard to win," said Muliaina. "You've seen over the last couple of weeks there's been two tight games and we've yet to see what the Aussies have got.
"We're going to go away and hurt for a week or so and watch that game and hopefully we can rectify some of the things that we didn't do too well.
"It's going to be a lot tighter Tri-Nations than it perhaps has been in the last few years."