They continued to dominate the match until the Old Boys' tight five, led by an inspirational performance by John Smyth, began to get the advantage.
"Our front row muscled up and we steamrolled their scrum a couple of times which gave us a bit more belief and we carried on from there," Matson said.
Old Boys fought back from a 20-31 deficit with 15 minutes to go to record the precious win. Their try scorers were Fisilau, Troy Gilbert, Dan Cotton, Saxon Samuels and Mateo Malupo.
Mid Northern coach Rick Caulfield said Mid Northern were overconfident after a good win over Marist in the previous round.
"It's a much closer competition this year so you have to be right on your game every week and we were a bit off ours on Saturday," he said.
"We let in too many easy tries; letting them score twice out of their own 22m just summed it up for us, so good on Old Boys, their attitude was better than ours."
Mid Western are now on top of the competition after beating the bottom-placed Otamatea 51-22 at Maungakaramea.
Wellsford are one point behind but they were made to work hard at Hora Hora, finally winning 20-10.
Kamo continued to gain momentum in the competition and moved up two places to third after humbling Marist 41-3 at the Kamo Rec, while the Western Sharks beat Hikurangi 24-14 at Dargaville.
Mid Northern slip to fourth ahead of Marist and Old Boys in fifth and sixth respectively, with the Sharks, Hikurangi, Hora Hora and Otamatea rounding out the bottom four.