Substitute Gary Jones scored five minutes from time to earn Grimsby a vital home win.
Fellow strugglers Lincoln went close when Lee Frecklington fired wide, while Grimsby's Sam Hird had an effort blocked on the line by Hamza Bencherif.
Jones nodded home the winner after Imps keeper Ben Smith could only push away Danny Boshell's free-kick.
Lincoln's Scott Kerr was sent off in the dying seconds when he received a second booking after fouling Boshell.
Grimsby: Barnes, Bennett, Atkinson, Newey, Hird, Bolland, Hunt,
Boshell, Hegarty, North (Jones 64), Butler (Taylor 72).
Subs Not Used: Montgomery, Whittle, Till.
Booked: Bennett (69), Hird (76)
Goals: Jones (85)
Lincoln: Smith, Moses, Brown, Bencherif, Beevers,
John-Lewis, Kerr, Frecklington (Hand 79), Dodds (Ryan 73), Forrester, Wright.
Subs Not Used:
Marriott, Warlow, Hone.
Booked: Kerr (63), Hand (85)
Sent-off: Kerr (90)
Referee: Lee Mason (Lancashire)
Att: 5,533
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