Although the game pitted league against non-league, the gulf between the two sides was minimal given Grimsby's full-time status and their good form in the Conference this season.
Aidy Boothroyd acknowledged that afterwards when he said: "It was going to be a difficult game from the start, we knew that," said Boothroyd after his side's second-round exit at Blundell Park.
"Grimsby are doing well in the league and there are not a lot of spaces between us."
Having seen their conquerors draw Huddersfield Town at home in the third round, Northampton know they have not missed out on a money-spinning draw and do have a major battle of their own to concentrate on now at the foot of League Two.
That does not lessen the disappointment at the manner of defeat at Blundell Park, however, Boothroyd commenting: "We set out with a game-plan to frustrate them, to stop them and to break on them. We did that and I really couldn't see any real danger apart from a set-play, which we work on all week.
"But one man loses his marker and it's just a really, really poor goal to concede. The game then changes because you've got to chase it and then it's finished."