The Lions secured all three points and moved up to 16th in the Championship thanks to Aiden O'Brien's goal midway through the second-half, with Leeds boss Thomas Christiansen admitting that "Millwall deserved this win."
Wolves continue their impressive start
Diogo Jota continued his impressive start to life as a Wolves player with a brace away to Nottingham Forest as Nuno Espírito Santo's side moved level on points with table-toppers Leeds.
Jota's fourth and fifth goals of the season consigned Forest to defeat, although they had pulled themselves level for six minutes through Mustapha Carayol's 75th minute strike.
The Owls took the lead through Gary Hooper's fourth goal of the season as they dominated the first-half, before Bamba's dramatic equaliser salvaged a point for Neil Warnock's side, who described it "like winning a game."
The R's took the lead early on through David Wheeler's first goal for the club before Lewis Baker equalised with his first Boro goal late on in the first-half.
Jamie Mackie put the visitors back in front as he capitalised on a defensive mix-up to tap in to the embarrassment of Boro keeper Darren Randolph, before two goals in five minutes from Ashley Fletcher and Assombalonga secured three points and propelled Middlesbrough to seventh in the league.
Blades slip to defeat at Bramall Lane
Sheffield United's winning run at home came to an abrupt end at the hands of Norwich City via Yanic Wildschut's first-half strike, with Blades boss Chris Wilder sent to the stands midway through the second period following an altercation with some water bottles at pitchside.
Daniel Farke's described his first away win as Norwich boss as "good for our confidence and the general togetherness" as the Canaries moved up to 12th in the table.
Ipswich Town moved up to fifth in the table with a win over rock-bottom Bolton Wanderers as Cole Skuse netted his first goal since April 2015 via a deflection before David McGoldrick made sure of the win in the 89th minute to get the Tractor Boys back to winning boys.
Bobby Reid remained the Championship's top-scorer as he netted his sixth of the season from the penalty spot in the Robins' 4-1 win over Derby County at Ashton Gate.
The Rams took the lead through Matěj Vydra's fourth of the season from the penalty spot after Robins keeper Frank Fielding brought the Czech striker down.
Lee Johnson's men turned the tide in the second-half as Cauley Woodrow, Reid, Jamie Paterson and Famara Diedhiou all netted to see Bristol City move eighth in the league.
Harry Redknapp pays the price for Blues' poor start
Barnsley's 3-0 defeat against Aston Villa at Oakwell saw them drop to 20th in the table as Albert Adomah continued his goalscoring form with a brace that means he now has three goals in his last three games, while Keinan Davis also netted to complete the rout.
Birmingham's defeat at home to Preston North End proved to be Redknapp's final game as manager despite Maxime Colin putting them in front 35 minutes in, before three goals in 11 minutes from Daniel Johnson, Jordan Hugill and Tom Barkhuizen ensured the Blues fell to their fifth straight defeat.
Burton Albion moved out of the bottom three with victory over Fulham thanks to goals from Stephen Warnock and Lucas Akins despite Oliver Norwood drawing the Cottagers level after half an hour, and the visitors were unlucky not to draw as Sheyi Ojo struck the post late on.
The day's two draws saw James Vaughan net his first Sunderland goal at the KCOM Stadium, although the Black Cats were denied late on by their former midfielder David Meyler's deflected strike to ensure the two shared the points.
The Royals levelled via Liam Kelly's spot-kick 20 minutes from time before Sone Aluko smashed the bar late on to leave Jaap Stam's without a win in their last two games.