Brig themselves ensured their NPL Premier Division status over the Easter weekend but with the pressure off they could not afford to ease up, with Mickleover fighting for their lives at the Sir Tom Finney Stadium.
Danny Forbes gave the Irongate hosts the lead in the 42nd minute.
But two goals in the closing stages of the game saved Mickleover and condemned Marine – who lost at Farsley Celtic – to the drop.
Shaquille McDonald netted from a 74th-minute penalty to level the scores and, five minutes from time, Evan Garnett scored Mickleover’s winner.
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Elsewhere in the division. Lancaster City were 2-1 home winners against Whitby Town, who led through Brad Fewster’s second-half strike.
Glenn Steel (72) equalised for the Dolly Blues and six minutes from time, David Norris hit the hosts’ second goal.
In the NPL West, Clitheroe drew 1-1 at home to Mossley, while Kendal Town went down 3-1 at Widnes.
AFC Fylde made nine changes – with one eye on the National League play-offs – at home to Halifax, and lost 2-0.
Southport lost 2-1 in the National League North at Blyth Spartans, Matthew Platt scoring for the Sandgrounders.
In the NWCL Premier Division, Burscough suffered a 3-2 defeat at Silsden.
And in the NWCL First Division North, their was last-day title joy for Longridge Town.
After slipping to second place in midweek, the long-time leaders knew nothing less than victory at home to Holker Old Boys – coupled with table-topping Avro losing at AFC Liverpool – would do.
And Lee Ashcroft’s men duly delivered, beating Holker 4-1, while Avro went down 1-0 on Merseyside.
And Garstang finished the season with a flourish, winning 4-2 at Shelley.
The victory secured a seventh-place finish for the Riversiders.