Scunthorpe United's last-ditch 3-2 victory at Accrington Stanley on Friday had meant that Chesterfield only sat top on goal difference heading into the weekend's encounter, and they made life difficult for themselves before claiming the win.
Shamir Goodwin gave the visitors the lead in the 50th minute and although Eoin Doyle equalised six minutes later, Chesterfield left it late to secure three points.
Jay O'Shea put the hosts ahead in the 80th minute and then added another in stoppage time, stretching Chesterfield's unbeaten run in the league to six matches, while Torquay remain second from bottom.
David Connolly got the first half's only goal just before the half-hour mark, before Nicky Wroe and Deane Smalley made sure of the comfortable victory in the second period.
The win sees Oxford's undefeated run in League Two extended to eight matches, while Mansfield stay six points above the drop zone.
Neal Trotman's 11th-minute red card helped York get a foothold as Wes Fletcher converted the resulting penalty after Ryan Bowman had been felled, and a double from John McCombe and Josh Carson's goal in the final stages saw York climb above Plymouth and up to 11th.
Rochdale picked up a second consecutive league win, coming from behind to triumph 2-1 over Morecambe, while Fleetwood Town also stayed in the hunt near the top of the table thanks to Gareth Evans' double in their 2-0 defeat of rock-bottom Northampton.
A 1-1 draw at home to Dagenham and Redbridge kept Burton Albion in sixth, but only seven points separates Gary Rowett's men from league leaders Chesterfield.
Cheltenham Town's home match with Wycombe Wanderers and Bristol Rovers' trip to Bury were both postponed due to waterlogged pitches.
