Abdullah Aswat hit the crucial goal for Soothill, who clinched the title after FC Bosnia could only draw 2-2 at Howden Clough.
Goals from Phil Crossland and Joe Armstrong saw Clough, who had man-of-the-match J Gash in fine form, lead 2-0 at the break.
The visitors battled back to draw level but taking just a point meant their title ambitions finally faded.
Last Thursday Bosnia had kept their hopes alive with a 3-2 home win over Soothill.
Semsudin Kalabic (two) and Haris Nicsic scored to give Bosnia the edge while Abdullah Aswat and Yusuf Dadhiwala replied as Soothill suffered their first league defeat of the season.
In Division One, Queensbury enjoyed a goal spree last Saturday as they won 7-1 at Ring Of Bells (Wayne Bromley).
Glen Kirk fired a hat-trick for the visitors whose tally was made up by Daniel Scrimshaw, Micky Boocock, Matthew Todd and an own goal.
Norfolk took a 2-0 lead against Inter Batley before running out winners 6-4. Norfolk goalscorers were Ilyas Lunat (two), Z Khan Shakeel Pandor, man-of-the-match Yanya Lunat, Younis Patel plus an own goal.