Winston finished 6-4-3 in his last three outings, enough to end the day marginally ahead of Columb but he only reduced the championship deficit by two points and it will take a huge dose of luck at Taupo in a fortnight if he is to snatch away the Kiwi crown.
The day's winner in the MX2 class was another Australian, Suzuki's Ryan Marmont - who managed 8-2-1 results at the weekend - but this was his debut appearance in the series and so he therefore has mathematically no chance of winning the title.
Meanwhile, in the 125cc class, Vaughan (Yamaha) had an up and down day, finishing third in both the day's early races as his main rival, Te Puke's Logan Blackburn (Yamaha) raced to victory and took over the championship lead.
But Vaughan struck back in race three, winning it in style as Blackburn struggled to fight through traffic and settled for fifth, promptly handing the championship lead straight back to Vaughan.
Just four points now separate these two young men as they head to Taupo and this class is one going down to the wire.