First-teamers Zak Mills, Andrew Boyce, Tom Bolarinwa, Harry Clifton, Josh Venny and Scott Vernon were named in the Mariners' starting Xl.
Town's first real chance came early on when some good work and delivery by Bolarinwa found the head of Scott Vernon who headed just over.
Bolarinwa was in the thick of the action again minutes later, latching onto a through ball and stinging the hand of Parkin in the Spireites goal.
Vernon did have the ball in the back of the net on 25 minutes, finishing well past the keeper, but the big striker was adjudged to be offside and the goal was disallowed.
But on 35 minutes, against the run of play, the visitors took the lead as German ran onto a through ball and finished past Heath-Drury in the Town goal.
The Mariners were still plugging away and Wright saw his effort turned away by Parkin.
Hough and Burchell were replaced by Goddard and Slater at the start of the second half for Town.
Tom Bolarinwa had the first chance of the second half but his free-kick sailed over the cross bar from 25 yards.
Harry Clifton had what turned out to be Town's best chance of the game on 49 minutes. The lively Max Wright won the ball in midfield and ran at the Spireites back line, before tapping the ball to Clifton who saw his effort go just over the bar.
Wright was again involved on 58 minutes, skipping past his marker before laying the ball off Slater who saw his shot blocked.
The visitors were to double their lead though on the hour. Bolarinwa did well to get in the way of a goal-bound effort, but the rebound fell nicely for German to tap home his and the Spireites second.
Town were still refusing to lay down and Vernon found Clifton with an inch perfect pass, but the young midfielder dragged his shot wide of the advancing keeper's post.
And a great individual effort by Bolarinwa, who skipped beyond two players before seeing his strike blocked.
Grimsby Town: Heath-Drury, Mills, Boyce, Hough, Lawis, Bolarinwa, Clifton, Venney (c), Wright, Vernon, Burchell.
Subs: Subs: Goddard, Sawyer, Slater, Lofts, Sesay.
Chesterfield: Parkin, Ofoegbu, Graham, Maguire (c), Daly, Beesley, Cartwright, Simons, German, Dennis, Gobern.
Subs: Rowley, Bronnell, Hand.