Gainsborough started brightly with attacking intent and in the 7th minute a pass from Lauren Crellin to the dangerous Grace Jones nearly led the opening goal but the shot was dragged just wide.
Five minutes later Jones returned the favour to Crellin but Belper goalkeeper Lucie Selby produced the first of several wonder saves for the afternoon as Belper's number one continued to impress since signing a couple of weeks ago.
Gainsborough continued to dominate without creating any further clearcut chances but there was bad news for Belper midway through the first half when Sky Hughes was forced off with a serious arm injury.
Selby produced a second magnificent save in the 28th minute, this time from Abbie Murrell's close range shot.
On 34 minutes Trinity broke the deadlock when a Katy Thornley cross from the left was deftly swept home by Jones.
In the 40th minute Murrell cut in from the left and fired off a shot which Selby did well to hold and then a minute before the break she was played through on goal but Selby rescued Belper once again.
The final action of the first half saw a cross from the left headed by Nadina Green but tipped wide by Selby.
The Nailers were struggling to create chances against a well drilled and organised Gainsborough side but four minutes into the second half a great ball by Alex Holland found Hollie Thompson who saw her shot saved by Isla Drewry.
In the 54th minute the home side doubled their lead. Hannah Layton, solid again in the right back position was penalised for a foul inside the box and Izzy Anderson stepped up to make it 2-0.
Belper settled down during the middle part of the second half with substitutions keeping things fresh, particularly in the midfield area.
The points were sealed on 78 minutes when Jones collected the ball 22 yards from goal and fired a great shot past Selby to make it three.
With ten minutes remaining Heather Gardener tried her luck from range but Selby's handling was impeccable once more, and it was the same again in the 85th minute, this time the shot coming from Crellin.
The final goal came three minutes into injury time when Leah Longdon was penalised for handball - harsh on the fullback who was an integral part of a hard working backline for Belper. Anderson scored her second penalty of the afternoon to complete the action.
Manager Dom Anderson had this to say: "At this level there are games we can win and there are games that we have to graft, be competitive and learn from. As Manager I think we hit that objective today.
"I was very happy to be told by the Gainsborough Manager that they found us the most difficult team to play against and break down.
"Lucie Selby took the Player of the Match awarded by both the opposition and BTFC media team after some unbelievable saves and Hannah Layton received the award from myself and Luke for some incredible last ditch tackles and adjusted well to some very good players".
Elsewhere in the division, Chesterfield won at 1-0 at Arnold Eagles while Dronfield and Grimsby Borough shared the points. Notts County drew 1-1 with Grimsby Town and Sherwood defeated Buxton 4-1. Gainsborough move five points clear at the top while Belper drop to 8th, with a crucial clash at Arnold Eagles - who sit level with the Nailers on six points - to come next weekend.
The Reserves were defeated 8-1 away to Castle Donnington and sit 4th in the table.
Gainsborough Trinity: Drewry, Carte, Deakin, G. Jones, Thornley, Murrell, Anderson, Green, Gardener, Crellin (C), J. Jones.
Subs: Hill, Leslie, Sykes.
Belper Town: Selby, Layton, Pickard (C), Claxton, Longdon, Thompson, White, Holland, MaCluskey, Hughes, Wilson.
Subs: Needham, Buxton, Bancroft.
Referee: Mark Raisborough