Jacob Hazel was the match-winner for the reserves on Tuesday afternoon, scoring the only goal of the game at Oldham.
Hazel, who was playing as a lone striker, slotted the ball past the keeper around the hour-mark after being put through by Mark Randall.
Randall himself went close with a couple of efforts, including one which clipped the bar.
Dutch trialist Etienne Esajas put a free-kick just off-target and substitute Jack Waddle threatened with a header.
Oldham improved late in the game without seriously testing Ben Wilson, on loan from Sunderland, in the Chesterfield goal.
Reserve-team boss Mark Crossley declared himself “very pleased” with the performance, adding: “We kept the ball well in the first-half and tried to play as much football as we could in difficult conditions.
“It’s a step up for the younger players and we’re seeing an improvement from them in every game.”
Esajas made his first appearance since linking-up with the Spireites. Commenting on the former Sheffield Wednesday star’s performance, Crossley said: “He played on the left and showed what ability he’s got but he still needs games.”
Craig Clay featured at right-back in a youthful back four alongside Jack Broadhead, Tim Whittaker and Matthew Clarke. Jonatha Wafula was on the right-wing with Mark Allott, Danny Whitaker and Mark Randall in the middle.
Line-up: Wilson, Clay, Broadhead, Whittaker, Clarke (Slack 60), Wafula (Fereday 75), Allott, Whitaker (Waddle 60), Randall, Esajas, Hazel