Chesterfield suffered a disappointing setback in their play-off push as they were beaten 3-0 by Oldham Athletic at the SMH Group Stadium.
Former Spireite Kane Drummond proved the difference, scoring twice against his old club, while another ex-Chesterfield player, Mike Fondop, also got on the scoresheet in a clinical away performance.
Oldham took the lead midway through the first half when Drummond controlled a cross from Jack Stevens before firing low past Zach Hemming in the 22nd minute.
The visitors doubled their advantage just nine minutes later, with Fondop calmly chipping Hemming after latching onto a long ball forward from goalkeeper Mathew Hudson.
Chesterfield struggled to respond and created limited opportunities, with efforts from Armando Dobra and James Berry failing to trouble the visitors significantly.
Oldham sealed the win in the 74th minute as defensive lapses allowed Oliver Hammond space to square the ball for Drummond to tap home his second of the afternoon.
The result sees Oldham extend their unbeaten run to eight matches and move within four points of Chesterfield, with two games in hand — tightening the race for the play-off places.
