The Swans do have a game in hand, but struggled to a 1-0 win over Bristol Rovers on Saturday - winning only thanks to a twice-taken penalty from Lee Trundle.
Yeovil Town now occupy the final automatic promotion spot, thanks to Batosz Tarachulski's 84th minute winner against rapidly-fading Wycombe.
Leyton Orient drop to fourth after being helf at Chester, while Southend demolished Oxford 4-0 and are in fifth place.
Macclesfield and Boston take the final two play-off positions, with the Pilgrims putting bottom-club Kidderminster to the sword at Aggbrough in a 4-0 win.
Managerless Notts County found some cheer to end a tough week, with a 3-0 win over Shrewsbury - leaving the Shrews just two points above second-bottom Cambridge, who were beaten at Rochdale.
Lincoln left it late to beat Northampton, with substitute Marcus Richardson grabbing a 90th minute winner to sink Northampton.