Doncaster Phoenix delivered what could prove to be the killer blow to their North One East rivals when they ran in five tries on their way to a 32-8 victory over third placed West Hartlepool at Castle Park.
More crucially, second placed Morley – who have two games in hand over Phoenix but are now 23 points adrift – suffered their first ever defeat at Pocklington where a late try gave the home side a 17-10 win.
Fly-half Jason Lennard scored early for Phoenix who were 22-8 up by half time thanks to further tries from winger Ed Miles and centre Dave Hankinson and a penalty from Lennard.
The visitors enjoyed plenty of possession against the league leaders but struggled to create much against an excellent Phoenix defence.
Full-back Dan Porter and prop Tom Bagnall completed the job for Doncaster with two late tries to seal a fine win.
Phoenix are hoping to seal back-to-back promotions after winning Yorkshire One last season.
Their next game is a local derby at Wheatley Hills on Saturday, March 5.
Wheatley dropped another place in the table – and they now have only two sides beneath them – after they went down 26-10 in their North One East match at Driffield.
The visitors were well in the game at half time, prop Jack Clayton and winger Dave Laycock scoring unconverted tries to leave a 14-10 deficit at the break.
But a decision early in the second half to go for a try rather than kick for goal from a penalty proved a turning point, with the hosts breaking away to score and condemn Hills to defeat on a difficult and windy afternoon.
Wheatley, in 12th, have a nine-point cushion between themselves and bottom club Beverley.