Graham Henry's side underlined their status as the tournament's red-hot favourites with a crushing 42-11 victory over hosts France in Auckland on Saturday.
Thorburn, who enjoyed two spells as a national selector in 1992-1993 and 2000-2001, believes the All Blacks' invulnerability will make them unstoppable this autumn.
"Undoubtedly, New Zealand are on the right track for the World Cup," said the USA Eagles head coach.
"I'm still pretty close to a few of the guys in the camp and they tell me they are well and truly on track.
"In the World Cup you need to play three good games in a row and I wouldn't put my money on anyone else beating New Zealand at this stage.
"I honestly can't see any side getting the better of them. No other team has a good enough attack to beat them.
"All the All Black forwards handle like backs, their scrum is outstanding with the line-out the only slight chink in their armour.
"But then how many tries have been scored against them at line-outs over the last 18 months? Not many. Their defence is phenomenal, too.
"It would take odd circumstances for them not to win the World Cup - and they'll probably shoot me for saying that."
Talk of Kiwi invincibility is nothing new with New Zealand backed equally heavily to win the 1999 and 2003 World Cups.
But on both occasions they were the victims of shock semi-final defeats to France and Australia, respectively, and their ability to produce at defining moments is still questioned.
Thorburn, however, believes other factors explain their lack of success since winning the inaugural World Cup in 1987.
"The choking aspect is absolute rubbish. These guys play in top-level competitions month after month," he said.
"They're used to the pressure. The reason they didn't do well in the last World Cup was selection problems.
"They left key players behind who were experienced, such as Christian Cullen and Anton Oliver, while bringing in guys who had never even played representative rugby.
"I know about this because I was involved in selection a year or two before. Some of these guys cracked under pressure in the semi-finals. In 1999 it was France's day."