Walsall moved back to within three points of League One's automatic promotion places on Tuesday with a 2-1 victory over struggling Shrewsbury Town.
A 4-0 defeat to Bradford City on Saturday had enabled Millwall to climb above Jonathan Whitney's side, but Walsall bounced back with a comfortable win in their game in hand.
First-half goals from Kieron Morris and Rico Henry sealed all three points to give Walsall hope of a top-two finish with two games to go.
In the Championship, Hull City made it five games unbeaten as mid-table Brentford were brushed aside 2-0.
A Harlee Dean own goal had given Steve Bruce's side the lead just after the half-hour mark and Mohamed Diame doubled their advantage on the brink of half-time - albeit after Adama Diomande had missed a penalty for the hosts.
Meanwhile, Portsmouth secured their play-off place in League Two thanks to a 1-0 triumph over AFC Wimbledon.
Michael Smith struck the decisive goal as the 2008 FA Cup winners moved nine points clear of eighth-placed Cambridge United with two to play, but Wimbledon still need a win to guarantee their spot.