It was a tale of two halves as Boro tasted defeat at The Den.
After largely dominating the first 45 minutes, albeit without creating gilt-edged opportunities, the Teessiders were undone after the break.
The hosts scored what proved to be the only goal 20 minutes into the second half as Boro returned home without a point.
Possession
60%Shots
11Shots On Target
4Corners
4Fouls
81
0
Cards
0
0
Millwall had an early opportunity when Tristan Crama headed wide from a free-kick, but the first half was one Boro had the best of.
It proved difficult to turn possession and territory into clear-cut openings, despite the Teessiders winning the midfield battle and providing a threat from wide areas.
Hayden Hackney dragged wide after bright play by Samuel Iling-Junior, who also teed up a Delano Burgzorg shot which was charged down by Jake Cooper.
Three minutes before half-time, Anfernee Dijksteel forced his way into the box and found Morgan Whittaker, who had a low strike saved.
There was nothing to separate the sides at the break, though.
Millwall: Jensen, Leonard, Crama, Cooper, Bryan, Honeyman (Neghli 58'), De Norre (Saville 58'), Mitchell, Emakhu (Azeez 58'), Ivanovic, Cundle (Langstaff 45')
Subs: Azeez, Wintle, Langstaff, Saville, Drake, George Evans, Harding, Matthews, Neghli (Harding 79')
Middlesbrough: Travers, Dijksteel (Iheanacho 84'), Howson, van den Berg, Iling-Junior, Morris, Hackney, Whittaker (Forss 66'), Burgzorg (McGree 66'), Azaz, Conway
Subs: Barlaser, Fry, McGree, Iheanacho, Forss, Glover, Giles, Woolston, McCabe
Millwall came out strongly in the second half and there was a flurry of early goalmouth action.
Boro scrambled a dangerous free-kick clear before Dijksteel blocked from Aidomo Emakhu and Mark Travers produced a strong hand to deny George Honeyman.
Travers also scooped away a Langstaff header as the hosts continued to threaten, but Boro gained a foothold and had an effort of their own through Hackney which went wide.
Millwall came back strongly, though, and after Femi Azeez whistled one not far past the post, his fellow substitute Camiel Neghli put the hosts in front with a clinical finish.
Boro attempted to find a response and went close when Finn Azaz’s long-distance hit took a deflection on its way narrowly over the crossbar.
Jonny Howson also saw a strike from range held by home goalkeeper Lukas Jensen and Azaz whistled another one just over from 25 yards.
We continued to search for an equaliser, but Millwall largely restricted Boro to efforts from distance, with Marcus Forss fizzing another of those over from the right of the area as the game reached its closing stages.
Two minutes into stoppage time, Forss was denied by a tremendous Jensen save as Millwall held firm to secure maximum points.
