In the intervening weeks, Yamaha's Smith successfully completed his New Zealand Cross-country Championships title defence, finishing that day near Norsewood more than half a lap ahead of his nearest challenger, but now his attention switches back to the enduro scene.
Smith is one of perhaps just a handful of riders capable of matching Birch, with Whangamata's former national enduro champion, Jason Davis (KTM), Auckland's Callan May (Yamaha), Tauranga's Reece Burgess (KTM) and Tokoroa's multi-time former national champion Sean Clarke (KTM) among the others most likely to feature near the front in the Maramarua Forest on Saturday.
With his four-event winning-streak, Birch has a tight grip on the top spot in the battle-within-a-battle for expert over-300cc four-stroke class honours, with Burgess his nearest threat 16 points behind.
Smith's outright runner-up finish at Waimiha saw him leap back to first-equal position in the over-200cc two-stroke class, a position he now shares with Davis.
Clarke sits on top of the veterans' (over 40 years) division, a safe 29 points ahead of his main challenger for class glory, Taupo's Mark De Lautour (KTM). Auckland's Freddie Milford-Cottam (KTM) leads the battle for bragging rights in the expert under-200cc two-stroke class.
BikesportNZ.com rider May had a tough time of it at Waimiha, at one stage crashing heavily into a tree, but he still managed to finish the day sixth overall, finishing top of the expert under-300cc four-stroke class and increasing his lead there.
After the Maramarua event, the series heads to Taupo for round six on July 20. It wraps up near Tokoroa on September 21.