Saints led 4-0 at the break and substitute Jamal Stewart struck a hammer blow for United with a second-half hat-trick.
Sean Fitzpatrick and Laurie Power bagged goals braces and a goal from James Reubenson Burgess completed the rout.
Horsforth are 10 points clear at the top after 24 games and their challenge for the title was aided by second-placed Farsley Celtic Junior’s surprise 4-3 home defeat to mid-table Leeds City.
Danny Lyons (2) and Said Osman were the scorers for Celtic with Tom Evans (2), Adam Fox and sub’ Desmond Okoro netting for the victorious visitors.
Thomas Ramsden, meanwhile, hit four as Littletown returned from Athletico with a 5-3 win under their belt, Nathan McDaid adding the other goal.
Zak Khan was another four-star performer, netting four times in Route One Rovers’ 8-2 triumph over visiting Calverley United. Danny Hussain, Mohammed Bilal Sadiq and Anees Younis were also among the goals for Route One. Lowly Lower Hopton - they’ve amassed only 12 points all season - made a decent fist of things at Stanley United but eventually came up just short, losing out 2-1.
Rhys Bruce and Adam Hayton hit the mark for United with Ben Wilson the scorer for Lower Hopton.
Toller closed the gap on visitors Alwoodley to two points on the league ladder with a 3-1 win.
Matters are really coming to a boil in Division 4 where second-placed Mount St Marys Reserves are turning up the heat on leaders Calverley United.
St Marys edged hosts Farnley Sports 4-3 thanks to a brace of goals apiece from Mark Giddens and Robert Hendry.
Mount are just three points off the pacesetters but, crucially, still have two games in hand in which to overhaul their title rivals.
And the two are scheduled to go head to head this coming Saturday ...
Meanwhile, bottom club Thornesians Reserves - without a win from any of their 18 games to date - crashed 11-0 at third-placed Leeds Modernians.
Grahame Stockdale struck for visitors Morley Town III in the opening 10 minutes of each half to secure a 2-1 away win over North Leeds Reserves.
Elliott Harris kept North Leeds in contention with a goal in the first half.
Joseph O’Reilly scored twice in the opening 20 minutes with Farayi Guzha adding to the tally on the hour and Michael King crowning a fine day for the hosts with a winner two minutes from time as Old Centralians overcame stubborn visitors St Bedes Reserves, 4-3.
In the Premier Division, Collegians drew 1-1 with Morley Town, Mount St Marys and Middleton scored two apiece, resurgent Nostell MW overcame hosts St Bedes 4-2, Stanningley OB scored three but were hit for six by visitors Golcar United, and White Rose edged out visitors Ealandians 3-2.
In the Championship, Gomersal & Cleckheaton were still in the mix at 1-1 on the turnaround, but hosts Colton Athletic rallied to win comfortably 4-1.
Elsewhere, Horsforth St Margarets Reserves smashed Crofton Sports 7-0, TVR United overran hosts Idle 8-1, Leeds Medics & Dentists Res triumphed 7-1 at home to Hanging Heaton, and Beeston Juniors beat Woodkirk Valley 3-0.
In Division 1, Beeston St Anthonys snagged the solitary second-half goal to take a share of the spoils from their encounter with visitors Athletico Reserves who had led 3-2 at the break.
Elsewhere, Morley Town Reserves edged Fairbank United 3-2 and Leeds City Reserves emerged from their trip to Thornesians with a 1-0 win as reward for their efforts.
Division 2 leaders Wortley Reserves made light work of their trip to Littletown Reserves - beating the third-placed team 9-1.
Trinity ASOB netted twice but were hit for six by visitors North Leeds, Ryburn United Reserves edged Norristhorpe 2-1, Sandal Wanderers were on the wrong end of a seven-goal thriller as they were pipped 4-3 at Huddersfield Amateur, and Dewsbury Rangers were involved in a 3-3 draw with visiting Leeds Medics & Dentists III.
The first half of Norristhorpe Reserves’ Division 3 home encounter with Morley Town U21s gave no hint of the goals avalanche that was to follow.
The sides turned around all square at one apiece but the hosts went on to win - 5-4.
Elsewhere, Garforth Rangers were held to a 3-3 draw by visitors Shire Academics III after leading 2-1 at half-time, Ealandians III were beaten 4-1 at home by Stanningley OB Reserves, and Savile United held the nap hand at Colton Athletic Reserves, winning handsomely, 5-2.
In Division 5, Ryburn United Academy scored seven unanswered goals at St Bedes Academy, Beeston Juniors Reserves defeated Old Centralians Seconds 5-0, while Crofton Sports Reserves enjoyed a 6-2 success over visiting Huddersfield Amateur Reserves.
Colton Athletic III, meanwhile, were edged out 2-1 on home turf by West End Park, and Leeds City IV and Shire Academics IV shared six goals evenly in their encounter.
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