D/L method struggling to keep up with powerplays?

I couldn't agree with Daniel Vettori more. How can New Zealand lose 5 overs, including 2 Powerplay overs, in their chase against Australia, and only get 8 runs knocked off their target? Australia scored 41 in their 5 batting powerplay overs (9, 9, 6, 8, 9) so I find it difficult to see how that was worked out. Anyone clever/mathematical wish to explain? Thought not!!