Unbeaten Malton and Norton marched on with a 32-12 home victory over neighbours Scarborough.
Centre Tom Maka touched down twice, and other tries came from No 8 Mark Bradshaw, winger Tom Newitt and centre Ryan Lonsdale.
Sheffield are still in second place but after their 23-7 defeat at Keighley are now just one point ahead of Heath, who won 35-25 at home to Bridlington.
Keighley went ahead with a try by right winger Lucas Uren after 12 minutes, Alex Brown converting, and although Sheffield soon equalised with a try by second-row Tom White, converted by Joe Cribley, that was to be their only score in their worst performance of the season.
Brown put the home side 10-7 ahead at half-time with the first of his three penalties, and also converted a second-half try by inside centre Marco Ferrazzano.
A try in stoppage time by scrum-half Steven Seed saw Knottingley force a 10-10 draw in their home match against Selby.
Selby had turned round 7-0 ahead following a try by scrum-half Matty O'Connor, converted by Jordan Barton.
Barton added a penalty early in the second half, and it was not until the 70th minute that Knottingley scored their first try through replacement Dave Sonia.
Slack tackling by the home side let Castleford in for a 30-15 win at Dinnington.
Ian Mattison converted all three tries – by Chris Brown, Will Nutbean and Gareth Paul – as well as landing three penalties.
Winger Mike Smith scored a first-half try for Dinnington, who added another by full-back James Marsden in the last two minutes.
Tries from Dan Watson, Nathan Dakin and Steve Moon, who also kicked two conversions, helped North Ribblesdale to a 19-15 win over Bradford Salem.
And Jarrod Morris and Luke Clougher scored two tries each as Heath beat Bridlington 35-25.