King William took the lead when striker Danny Gray cut in from the edge of the box and fired into the top corner of the net.
They had to wait until the stroke of half-time for their second, which was scored by Mitch Carter. Neil Ducey made it 3-0 just after the break before Liam Summers pulled a goal back for the home side.
King William restored their three-goal lead straight from the kick off when Carter scored his second.
Ducey bagged his second after an 18 pass move and, eight minutes from time, Carter completed his hat-trick.
Second-placed Wigginton Grasshoppers, who are level on points with the leaders having played five more games, were 6-1 winners over Enterprise.
Jack Coates’ bullet header gave ’Hoppers the lead after ten minutes.
Tom Nicholson and MacKenzie Nichol scored before half-time and then Michael Clancy and Jordan McGuigan scored penalties either side of an Enterprise spot kick converted by Matthew Pallister.
Nicholson added his second to round off the scoring.
In division two, Beeswing got their first win in ten games by beating basement side York Medics to move out of the relegation places.
Medics were denied the lead when Wing ’keeper Paul Huttinson saved a penalty.
A 25-yard free-kick from Callum McKenzie gave Beeswing the lead, but Medics hit back with two goals to lead 2-1 at the break.
A strike from Paul Crangle made it 2-2 before new signing Anthony Evans scored Wing’s match-winner.
Albion Vaults kept their promotion hopes alive after coming from behind with a brace from substitute Dave Hulla and a Daniel Hewitt strike to win 3-1 at Hemingbrough.
Marcia Grey opened up a six-point lead in division three after thumping visitors Brayton 7-1. A first half hat-trick from Carl Stewart put the table-toppers 3-0 up at the break.
Substitute Paul Harris hit the target twice before Brayton got on the score sheet in the 64th minute with a goal from Rob Guest.
Harris then completed his hat-trick and Stewart completed the scoring with a 40-yard lob.
They went 2-0 up midway through the second half with a Joe Darnton strike, the third coming from Daniel Phillis minutes later. United grabbed a late consolation.
Snaith are champions of division four after thumping Eggborough Rangers 8-2.
Station are through to the semi-finals of the League Cup after edging past Huntington Rovers 7-6.
Gary Collier hit five goals for Station, while Craig Allen and Luke Durham also scored.