Swansea held onto the top spot with a 2-2 draw at Tranmere, which keeps them above Huddersfield on goal difference.
Jake Robinson equalised two minutes from time to earn the Welsh side a point.
The Terriers are now level with them on 38 points thanks to their 2-1 win over Nottingham Forest.
Danny Schofield and Andy Booth scored the crucial goals, with Jack Lester – later sent off – getting Forest's consolation early in the second-half.
Southend remain third, but now trail the top two by five points after their 2-1 defeat at Port Vale.
Leon Constantine put the home side ahead after 18 minutes, with Michael Husbands doubling the advantage before Jay Smith pulled one back in the final minute.
Chesterfield were held to a 1-1 draw at Saltergate by a rejuvenated Blackpool side, with the big talking point being the dismissal of Pool's Ciaran Donnelly and the Spireites Shane Nicholson early in the match for violent conduct after a clash.
Barnsley hammered bottom club Swindon 3-0 at the County ground, thanks to a Martin Devaney effort and brace from Chris Suker, to stay in the play-off positions.
Colchester moved up to seventh after a 5-0 drubbing of Gillingham, with Greg Halford and Jamie Cureton plundering two goals each.
Mark Tinkler fired Hartlepool to a 1-0 win over over Bradford at Valley Parade.
Doncaster beat Bristol City 2-0, while Walsall overcame Rotherham 3-1.
MK Dons lost to Bournemouth, and Oldham beat Yeovil 2-0.