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:
1. Marcus Bettinelli - 7
Didn’t have much to do but was vocal throughout and made a sharp save to deny Ben Thompson’s header in the second half. 7 Photo: Alex Pantling
2. Anfernee Dijksteel - 7
Solid on his return to the side as Boro looked comfortable at the back. 7 Photo: Clive Brunskill
3. Paddy McNair - 8
Almost scored a fourth goal for Boro with a powerful free-kick. Helped drive his team forward in the first half when stepping out from the back. 8 Photo: Alex Pantling
4. Dael Fry - 8
A comfortable first half as Millwall offered little in the final third. Had to deal with towering frontman Matt Smith after the break. 8 Photo: PA