"I will still be pushing hard for the win at the final round even though I don't need to," 27-year-old Smith said. "I always race to win."
Te Awamutu's Mark Penny wrapped up the over-300cc four-stroke class title at the previous round but hopes to win outright on Saturday.
Smith and Penny have little left to prove, unlike riders locked in battles in other classes.
They include Maruia's Ethan Bruce, Raglan's Graeme Goodwright, Auckland's Sam Greenslade, Marlborough's Scott Orchard, Raglan's Matthew Quirke, Palmerston North's three-time former outright national champion Adam Reeves, Woodville's Ben Exeter, Onewhero's Jim Orton, Morrinsville's Simon Lansdaal Cambridge's Andrew Charleston and Raglan's round-one winner Jason Dickey.
The runner-up spots in the over-200cc two-stroke and over-300cc four-stroke classes are still being fought over and winners have yet to be determined for the under-200cc two-stroke and under-300cc four-stroke.
"It has been a great series, with a variety of tracks and conditions really testing the riders," said Motorcycling New Zealand cross-country commissioner Chris Smyth. "The course this weekend will be another interesting battleground."
The junior grade is also likely to be fiercely fought, with Cambridge's Taylor Rae, Eketahuna's Charlie Richardson, Pukekohe's Isaac Clark, Marton's James Galpin and Marton's Ethan Breuer among the leading contenders to win the 90-minute junior race in the morning.