Reynolds was trailing 5-2 in the second set when he saved two match points and fought back to win the second set 7-5 before taking the third 6-0.
In his quarter-final the Lindisfarne College Year 8 student was leading South Australia's Joonky Nah 4-0 in the first set when Nah retired with an injury.
The country's top-ranked 12 and under boy, Reynolds was the only Kiwi in action at the tournament.
"The Aussies have been fantastic to me. They let me hit up with them before the tournament and in warm-ups ... they have been great hosts," Reynolds said.
A son of former Hawke's Bay representatives Andrew and Louise Reynolds, Reynolds will play in the under-14 section of an Auckland tournament at Labour Weekend. Later in the year he hopes to be selected in the New Zealand 12 and Under team which plays at an Australian tournament in Melbourne.
The performance bodes well for Kiwi junior players, especially following the good results of Wanganui 15-year-olds Butters and Paige Hourigan as well as Auckland 15-year-old William Matheson and 16-year-old Alex Klintcharov, who competed strongly in tournaments in Holland recently, including a grade-two ITF doubles title with Hourigan.
Tennis New Zealand chief executive officer Steve Johns was delighted with Reynolds' result and how players from all parts of New Zealand were making an impact at junior level. "It's good to see Finn come through and beat the Australians in their own events. He's obviously got a lot of talent and there are also some other young players starting to make their mark. It's also good to see players from across the whole country putting in impressive results and competing hard against each other and overseas opponents too," Johns said.