Hikurangi led 12-8 at the break and then went 18-8 ahead with an early second half try. The Bulls lifted their game and went on their try scoring spree, adding two kicks to lead 24-18.
Despite some scares, they held on to win by the same margin.
"Steve Rau wound up for some massive runs but the boys made some big hits in defence to hold them out, and they stuck together when the pressure was on and that's what got us home," Selkirk said.
Prop Joe Paniora and hooker Tuaka Mau were the team's best players on the day, as the Bulls took a big step toward achieving their aim of being in the top three at the start of the playoffs.
"With four more games to go [until playoffs] we're now in great position to achieve that but, with all these upsets, we won't be taking that for granted," he said.
The form book was in tatters as City downed Takahiwai 32-20 and Hora Hora knocked over the in-form Portland 28-8, in what is shaping up as the most even competition in years.
Sam Henry Des Reynolds, Kurtis Tito, Tas Nathan and Scott Cameron were sensational, with the rest of the team not far behind as Hora Hora claimed their biggest scalp of the season in some style.
Hora Hora coach Sean Tito said the side have slowly been building their game and nearly everything they touched on Saturday turned to gold.
"They did what I've tried to drill into them. They didn't fight the tackles and completed the sets, and so we good ball in hand and really controlled the game," he said.
Tito said wins like the one on Saturday were important for the team's development by encouraging them to train harder and promoting a culture of success.
The Northern zone did not escape the upsets, with the Hokianga Pioneers proving that they are far from finished in the competition by knocking over Moerewa 38-24. The only result that went with the formbook was Muriwhenua Kuaka's 34-14 win over Kerikeri Slayers.