Grimsby boss Paul Groves finally saw his side win their first Cup tie of any description under his management - 1-0 against QPR.
But they left it till late before leading scorer Michael Boulding notched his 10th goal of the season in the 80th minute.
A cross from the left reached him and his left foot shot went beyond keeper Chris Day and nestled in the bottom corner.
The goal may have been late but the Mariners were full value for their avenging of a 1-0 home defeat in the league by Rangers a month ago.
Rangers hit by injury did not have an attempt on goal and, had Grimsby taken their chances, they would have won by three or four clear goals.
Striker Iffy Onuora headed against the bar after four minutes and then Boulding sliced wide.
Day denied midfielder Des Hamilton at the second attempt and then touched over a header from centre back Tony Crane.
In a match played in a strong swirling wind Grimsby took complete control and Rangers were unable to mount any attacks of any note.
The second half continued in much the same vain and left back Darren Barnard hit the angle of post and bar with a quickly taken free-kick.
Once again Rangers could not get any serious attacks going and any high balls into the box were comfortably dealt with by centre back Crane and Michael Edwards.
The longer the game went on and it remained goalless Rangers must have fancied their chances of taking Grimsby back to Loftus Road for a replay, but that would have been rough justice on a lively Grimsby side who, on the day, carried too much strength and skill for the injury hit Londoners.
Because of Rangers' injuries and another one sustained by midfielder Martin Rowlands, manager Ian Holloway was probably just relieved to get the match out of the way so he can concentrate on a promotion push.