Spearman-Burn is in a group of players in a tie for eighth on even par and could be heading for his biggest career payday.
Michael Hendry's mixed back nine caused him to slide down the leaderboard as one of the pre-tournament favourites lodged three birdies, two bogeys and two double bogeys.
At one point this afternoon, Hendry held the outright lead of the tournament as the Aucklander birdied three of the first eight holes but he eventually signed for a two-under 70 to be four shots behind Brown in a tie for fourth with veteran Australian Peter O'Malley.
Australian Jason Norris equalled Brown's round of 66 but his six-under score only erased the shots he had dropped during his first two rounds and he is also in the group of players at even par.
Of the other Kiwi hopefuls, Richard Lee fired a two-under 70 to be at even par for the week and Brad Shilton is tied for 14th at one-over.
Pearce shot a frustrating two-over 74 to be in a share of 21st at two-over the card, alongside Phil Tataurangi, who signed for a 69 - his best round of the week - and Ryan Fox.
Gareth Paddison and Mathew Perry both shot 75s to drop back to two-over for the tournament with Pearce, Fox and Tataurangi.
Tasmania's Clint Rice provided the shot of the day when he aced the par-three ninth hole with a six iron from 177m - it was the fourth hole in one on the Australasian PGA Tour this year.