MIDDLESBROUGH slipped to defeat in the capital as Millwall ran out 3-1 winners at The New Den.
A brace from Andy Keogh after an opening goal by Liam Trotter was enough to see off the Teessiders, who scored themselves just before half-time through Marvin Emnes from the penalty spot.
Millwall bossed the early stages of the game at The New Den, and opened the goalscoring on 25 minutes when Trotter shot from 20 yards past Jason Steele .
And it was worse for Boro ten minutes later when goalscorer Trotter's shot beat Steele again, hit the post and Keogh was on hand to slot in the rebound.
Boro reduced the deficit two minutes before half-time after George Friend was scythed down in the box by Jimmy Abdou after the Boro full-back ran 80 yards to meet Emnes' pass. The Dutchman stepped up to take the penalty and slotted it into the right corner of Maik Taylor's net.
Despite the goal, Boro did not really kick on in the second half, and while they offered a sporadic goal threat, it was Millwall who looked more likely to score, when on 52 minutes they spurned an opportunity following James Henry's drilled free kick which Keogh couldn't make count.
Friend, keen to get forward, had a shot deflected out for a corner on the hour mark after Emanuel Ledesma's perfect diagonal ball, while at the other end Millwall's man of the match Trotter found Keogh, who squared for Josh Wright to shoot just wide of Steele's goal.
On 71 minutes, Josh McEachran shot across the face of goal, while seconds later a speculative header by Seb Hines dropped on to the roof of Taylor's goal.
But Boro's efforts were in vain as Millwall put the gloss on a well-deserved victory on 86 minutes when Keogh, signed from Wolverhampton Wanderers in the close season, scored his second when he converted Scott Malone's cross past Steele.
Almost immediately, Boro registered two quickfire chances when Friend shot at Taylor, while Emnes missed a sitter on the rebound when he scooped over the bar from inside the six yard box.
MILLWALL (4-4-2): Taylor; Dunne, Lowry, Osborne, Malone; Henry, Wright, Abdou, Trotter (Feeney 82); Henderson (Batt 46), Keogh. Subs: Forde, Shittu, Racon, Marquis, Batt, Feeney, Taylor.
MIDDLESBROUGH (4-4-2): Steele; Hoyte, Woodgate, Hines, Friend; Zemamma (Ledesma 56), Leadbitter, McEachran, Haroun (Smallwood 62); Miller (Williams 73), Emnes. Subs: McManus, Ledesma, Arca, Williams, Reach, Ripley, Smallwood.