The Lions responded after defeat on Easter Monday with a comfortable win over Preston North End, whilst Birmingham's unbeaten run came to an end at the Stadium of Light against Sunderland.
Match preview
Millwall ended their four-game winless run on Saturday afternoon by beating Ryan Lowe's Preston at The Den, with goals either side of the break from Tom Bradshaw and Zian Flemming securing a much-needed maximum.
Supporters were understandably worried after their men went a quartet of Championship matches without a victory, but - in part thanks to the inconsistency of their playoff rivals - Gary Rowett's men have managed to stay well in the hunt for promotion.
The Lions are currently fifth in the second-tier standings, three points better off than seventh-placed Coventry City, with the Sky Blues having won just one of their last four games.
Finishes between the positions of eighth and 11th over the past three campaigns will make Rowett's side wary of getting too carried away about their Premier League potential, however this season feels like a real opportunity for the club to reach the playoffs at least.
Having added attacking flair to their usual defensive solidity, Millwall look set to be in the top-six race right until the end, with goalkeeper George Long keeping three clean sheet in his last four outings.
Birmingham's four-game unbeaten run came to a disappointing end in the North East on Saturday afternoon against a Sunderland side aiming to achieve unlikely back-to-back promotions.
Tahith Chong came up with a moment of calm amongst the counter-attacking chaos to find George Hall as Blues took the lead after 29 minutes, however goals from Trai Hume and Amad Diallo meant John Eustace's side travelled back home with no points.
Having now reached the coveted 50-point mark in the Championship, the Second City club look all but safe from relegation to League One, with Birmingham eight points above 22nd-placed Reading with just 12 points left to play for.
Blues have failed to win on their last three visits to The Den but enjoyed one of their brightest days of their current 12-year stay in the Championship at Millwall, with Chris Hughton's men winning 6-0 against Tuesday's opponents back in January 2012.
That 2011-12 campaign was the last time Blues truly competed at the top of the Championship, however with a staged takeover of the club in the pipeline, Bluenoses will be hoping their team can challenge for promotion once again in the next few years.
Millwall Championship form:
W
L
D
D
L
W
Birmingham City Championship form:
L
W
W
D
D
L
Team News
Millwall continue to shine in the second tier despite injuries to key members of their squad, with Tyler Burey and Callum Styles both out of action with hip and muscle issues respectively.
Charlie Cresswell has not featured for the Lions since sustaining a head injury during his side's goalless draw at West Bromwich Albion - Jake Cooper and Shaun Hutchinson are set to be the central-defensive partnership for the hosts in this one.
Birmingham are hoping that the hamstring strain suffered by goalscorer Hall on Saturday is not one that will keep the youngster out until the end of the season - the midfielder will go for a scan on Monday ahead of a potential trip to Millwall.
Troy Deeney and Dion Sanderson are to step up their recoveries from hamstring and back injuries respectively over the next week, although Tuesday's match will come too soon for the pair.
Millwall possible starting lineup:
Long; McNamara, Hutchinson, Cooper, Malone; Mitchell, Saville, Burke, Flemming, Voglsammer; Bradshaw
Birmingham City possible starting lineup:
Ruddy; Colin, Roberts, Long, Trusty; Bielik, Hannibal, Chong, Bacuna, Khadra; Jutkiewicz
We say: Millwall 1-1 Birmingham City
Millwall face Birmingham, Wigan Athletic and Blackpool in their next three matches, and Rowett will realise his side have a good chance of securing playoff football before they welcome Blackburn Rovers to The Den on the final day.