The York club, who first won the trophy three years ago, stormed to a 20-4 victory at Pontefract to leapfrog Hallamshire – without a game this week and with only one fixture left – into top spot.
Dunnington now lead the Sheffield outfit by 19 points with two games to go and can clinch the trophy on Wednesday night when they face third-placed Queens, as they only need 14 more points.
The Halifax club, who also have two matches left and trail Dunnington by 27 points, kept alive their faint hopes of the title with a 15-8 home success against Chapel Allerton.
Dunnington were led to their sixth consecutive win by world no.23 Chris Simpson, who bounced back from his 3/0 Premier Squash League loss to German champion Simon Rosner the previous evening playing for Duffield with a straight-games win of his own against Alex Hodgetts at first string.
Gareth Lumsden also eased to a 3/0 win at no.2, against Lewis Doughty, while Ed Shannon, Matt Stephenson and Alistair England ensured a clean sweep for Dunnington with respective triumphs over Sam Wileman (3/1), Kyle Maree (3/1) and Stuart Hargreaves (3/2).
Queens’ win against fourth-placed Chapel Allerton was a more closely-fought affair, with James Earles tipping the balance by bridging a 50-position world ranking gap in overcoming world no.52 Eddie Charlton 3/0 at first string.
Matthew Sidaway and Connor Sheen ensured Earles’ hard work was not wasted with respective 3/1 successes against Dominic Hamilton at no. 3 and Niall McKinnon at no.4.
Declan James and Adam Wellstead gained consolation victories for Chapel Allerton against Patrick Rooney (3/0) and Irish national champion Madeline Perry (3/1).
Meanwhile, at the bottom of the table relegated Pontefract seconds scored a rare win – only their fourth of the season – by a 17-9 margin at Heaton.
They will be replaced by Abbeydale seconds next season, as they are runaway leaders of Division One.