Oxford beat 10-man Mansfield 3-1 at the One Call Stadium to take top spot in Sky Bet League Two while ambitious Fleetwood slipped out of the top three.
Sean Rigg opened the scoring for the U's after 12 minutes and, after Jamie McGuire saw red for the hosts midway through the first half, Lee Stevenson and James Constable exchanged goals in stoppage time.
Ryan Williams put Oxford two goals clear in the 66th minute and Chris Wilder's men now occupy first place in the fourth tier by virtue of a superior goal difference to Chesterfield and Rochdale, who both won their games.
While the Spireites downed Torquay 2-0 at Plainmoor thanks to first-half goals from Oliver Banks and Jay O'Shea, and Dale edged a 2-1 victory at Morecambe thanks to Mark Hughes' second-half own-goal - Scott Hogan and Padraig Amond also notching - Graham Alexander's Fleetwood were surprise 1-0 losers at bottom club Northampton.
It was only a third win of the season for the Cobblers as Luke Norris struck a last-minute winner at Sixfields. Adrian Boothroyd's men are still a point from safety.
Southend made their move towards the automatic promotion places, with third place now only three points away, by beating Exeter 2-0 in Devon.
It was a comfortable afternoon for the Shrimpers as Kevan Hurst followed up Cauley Woodrow's opener to wrap up the victory before half-time.
Dagenham breached the play-off spots with a 2-0 home win over Burton, Luke Howell and Zavon Hines on target as the Londoners set up camp in seventh place.
Neal Ardley's AFC Wimbledon were the afternoon's big winners as they thumped 2008 FA Cup winners Portsmouth 4-0 at Kingsmeadow.
Andy Frampton bagged a brace with goals either side of the break and Pompey, who are now 16th, looked helpless to resist as Sammy Moore and Michael Smith each helped themselves to a goal in the final eight minutes.
Accrington were shock winners at Scunthorpe, a 2-0 victory lifting James Beattie's team out of the relegation zone. George Bowerman and Kayode Odejayi grabbed the goals in the first half.
Elsewhere, Bristol Rovers were denied the chance to pull clear of the bottom two as Bury's Danny Hylton forced a 1-1 draw at the Memorial Ground.
John-Joe O'Toole had scored the first goal of the day when he fired home for Rovers in the fourth minute.
York and Plymouth are also scrapping at the wrong end of the table and an exchange of goals between Ryan Bowman and Tope Obadeyi produced a 1-1 draw at Bootham Crescent.