Sixth-placed Louth closed the gap on Rasen, who lie in fifth, to a single point with a tidy win at Rase Park.
Aaron Greenbeck was on the scoresheet for Town, but goals from Joe Marshall, Michael Broom and Rocky Rawlings helped the White Wolves bag their sixth league win of the season.
The derby defeat came hot on the heels of a 2-0 reverse at Lincoln Moorlands in midweek and continued their up-and-down season.
Rasen have beaten two of the top three this season, including a rare league defeat for leaders Skegness Town, but they have now lost as many matches as won after an impressive start.
They will be confident of getting back on track this weekend at second-bottom Ruston Sports who have won just once this term and lost eight of 11 fixtures. Kick-off is 3pm.
Immingham Town 3 Brigg Town Reserves 2
Brigg twice let a lead slip as Immingham Town bounced back to winning ways on Saturday.
The visitors drew first blood with a goal after 17 minutes before Carl Price’s penalty levelled the scores eight minutes later.
Brigg regained the lead seven minutes into the second half before Ben Cooke grabbed an equaliser for the Pilgrims On the hour.
Price then grabbed the glory with a winning goal two minutes from the end.
Brigg’s goals came from Jonathan Nichols and an own goal.
CGB Humbertherm 0 Skegness Town 4
Leaders Skegness Town were below their five goal-a-game average at Fulstow, but four was more than enough to secure three points.
Keeper Kaleb Robertson pulled off a couple of smart saves to deny the home side before Will Britton put the visitors in front.
Alex Nichols doubled their lead and then two own goals made the half-time score 4-0.
Humbertherm stemmed the tide after the break, but found the reorganised Skegness defence in defiant mood.
Lincoln Moorlands Railway 2 Nettleham 2
Nettleham went into the half-time interval with a two-goal cushion, thanks to goals from Shaun Booth and Liam Kishere.
But a neat finish from Simon Mowbray halved the deficit and the Railmen got back on level terms with a Lee Burke goal.
Grimsby Borough Reserves 1 Wyberton 0
For the third time this season a solitary goal was enough to secure three points for Grimsby.
This time round it was scored by Gareth Flint against Wyberton, who were led by new manager Joe Gresswell following Boston Town’s appointment of Gary Frost to the manager’s position.
The three points consolidated Borough’s third place in the table.
Harrowby United Reserves 1 Sleaford Town Reserves 5
Sleaford Town’s second string had to come back from behind to clinch the spoils at Harrowby United Reserves.
Louis Bland gave the home side the lead after just two minutes, but an Eddie Davies hat-trick and further goals from Corey Newman and Alan Forwood turned the game on its head.
The result lifted the Eslaforde Park outfit to 12th in the table.
Hykeham Town 5 Horncastle Town 2
Hykeham Town extended their winning streak to six games and went second with a creditable win over high-flying Horncastle.
A brace of goals apiece for Chris Funnell and Alex Mackinder helped their cause, as did Ben Good’s strike.
Horncastle’s goals came from Richard Jackson and Andrew Bullivant.
Ruston Sports 2 Sleaford Sports Amateurs 3
(abandoned after 67 minutes)
A serious injury to a Ruston player led to this match being abandoned midway through the second half.
Sleaford were leading 3-2 at the time, thanks to goals from Sebastian Firman, Liam Tunstall and Nathan Thompson.
Ashley Woodhall and Liam Barker had been on target for the home side.