Emmanuel Latte Lath’s eighth goal of the season moved Middlesbrough back into the Championship play-off places and ensured Neil Harris’s second reign as Millwall boss would end in defeat at the Riverside Stadium.
Harris, who announced last week the trip to the north-east would be his last in charge of the Lions, saw his side spurn golden first-half chances for Macauley Langstaff and Femi Azeez.
And after Latte Lath’s 10th-minute opener, Michael Carrick’s men went on to bounce back from their midweek loss at Leeds with three points without ever looking entirely convincing.
It might have been a different send-off for Harris had Langstaff – still looking for his first goal since his summer move from Notts County – not drilled a low shot straight at Boro keeper Sol Brynn after pouncing on a careless back pass by George Edmundson after seven minutes.
The visitors were punished three minutes later when a neat ball from Finn Azaz outfoxed Murray Wallace and let Latte Lath in to fire the opener past Lukas Jensen.
Boro suffered a setback when Luke Ayling was forced off with an injury on 22 minutes and the Lions missed a second golden opportunity when Azeez beat the offside trap but was again denied down low by Brynn.
The hosts had the better chances as the first half ticked towards its conclusion, Azaz slicing a shot wide on the end of a crisp counter-attack then Hayden Hackney drilling a shot at Jensen from a tight angle.
Millwall’s threat subsided in the early stages of the second half and a good defensive intervention from Casper De Norre prevented the ever-dangerous Latte Lath from adding to his tally.
Boro had a penalty appeal turned down after Ben Doak was challenged by Danny McNamara, and an unmarked Azaz slammed a shot wide from the edge of the box as Millwall left spaces in their push for a leveller.
Boro duo Tommy Conway and Delano Burgzorg came closest to snatching a second in the final stages before Harris was denied a dramatic send-off when Millwall saw a penalty appeal for handball waved away deep into injury time.
