Two goals from Duncan Watmore either side of a Marcus Tavernier strike inside 20 gave the Teessiders all three points after back-to-back defeats at Stoke and Preston.
Our Boro writer Joe Nicholson has dished out his marks from the match – scroll down and flick through the pages of our picture gallery to see how each player fared for the Teessiders:
5. Marc Bola - 7
Didn’t need to get forward much with Marvin Johnson causing problems on the left. Saw out most of his defensive duties. 7 Photo: Clive Brunskill
6. Sam Morsy - 7
Assisted Boro’s second for Tavernier. Kept it simple and held his position in midfield. 7 Photo: Alex Pantling
7. George Saville - 8
Constantly applied pressure and helped Boro win the ball back in the first half. Played a key part in the first and third goals. 8 Photo: Getty Images
8. Duncan Watmore - 9
Ran into goal-scoring positions and stretched the Millwall defence. Scored twice and worked his socks off. 9 Photo: PA