The win was trainer Mark Purdon's third Derby success this season, having won the NZ Derby with Fly Like An Eagle and the NSW Derby with Smolda.
But while that pair had huge reputations entering the autumn, Best Deal Yet was considered just a promising lower-grade pacer.
Since then he has won three times in Australia and three times at home for nearly $200,000 in stakes.
"Smolda is still our best 3-year-old but this guy has caught up to the rest of them," said Rasmussen.
Earlier on the night, veteran pacing hero Smoken Up had to settle for third after leading in the Sunshine Sprint, run down by former Kiwi pacer Motu Crusader.
In Auckland, 2-year-old pacer Bit Of A Legend warmed up for next month's Australasian Breeders Crown by beating the older horses at Alexandra Park yesterday.
He will join stablemates Chanelle Bromac and Onlyforyou in Cran Dalgety's team for the rich ABC series, but Sires' Stakes winner Texican will miss the series after his owners decided not to send him.
Other New Zealand-trained juveniles Border Control and Major Star will be hot favourites to win their ABC heats in Victoria tomorrow night, while Northern Oaks winner Twist And Twirl races in a heat on Wednesday night.