MIDDLESBROUGH’S faltering promotion hopes took another hit after defeat at Millwall saw Garry Monk’s men suffer a fourth loss in six matches.

Sloppy defending by the visitors allowed Jed Wallace and George Saville to score in six first-half minutes to leave Boro 2-0 down at the break.

Monk’s side improved in the second half and pulled one back through Stewart Downing’s long-range effort, but Millwall deservedly held on for the points to leave Boro five points off the play-off places.

The Middlesbrough manager said: "At the risk of repeating myself, it's just naive, it's extremely naive. We know coming here, we've prepared the players all week, the direct play it's going to be. That battle, that physical element to it, in terms of competing for those second balls, very direct stuff.

"To then be so naive and lose a lot of those battles in that first half in important areas and again in leading to the goals, it's naive, schoolboy stuff. I've said it too many times this season.

"It's never through a lack of effort within the group. It's just comes back to naivety. I feel like a broken record at the moment. Schoolboy errors, so avoidable and basic stuff.

"And you don't expect that from the level of players we've got, but unfortunately it's happening too many times this season, but we have no other choice but to work and try and come through it."

On a freezing cold south-east London afternoon, Monk named an unchanged starting line-up from the side that beat Ipswich Town, but it was Millwall that had the first effort of note, Aiden O’Brien hitting a half-volley well over from just outside the area in the fourth minute. At the other end, Patrick Bamford dragged a left-footed shot wide of the far post from 20 yards.

Boro had the best chance of the opening period in the 15th minute when Grant Leadbitter sent Downing scampering away down the right. He cut inside and teed up Bamford who saw his fierce drive come back off the near post.

A minute later, Darren Randolph unconvincingly bundled a Shaun Hutchinson header behind at a Millwall corner.

The Boro keeper redeemed himself in the 22nd minute when he made a fine one-handed stop from Lee Gregory’s close-range header after Hutchinson had nodded another corner towards goal.

Britt Assombalonga had the ball in the net in the 28th minute but saw his header from Downing’s cross correctly ruled out for offside.

It was the hosts who went in front in the 31st minute. Ryan Tunnicliffe picked up the ball in the middle of the park and his throughpass saw Wallace beat Boro’s static offside trap and race clear. Randolph came out to narrow the angle but Wallace slipped his shot under the Irishman’s body and in.

Things got even worse for the visitors in the 37th minute when Morison got down the right and cut the ball back for Saville. Despite a poor first touch, the midfielder somehow bundled his way through three lacklustre Boro challenges to score from close range.

It was almost 3-0 moments later when O’Brien broke from his own half and raced towards goal, with only a last-ditch block denying him. Daniel Ayala then had to be alert to stop Gregory from pulling the trigger after Boro had again failed to clear their lines.

Boro were sent out four minutes early for the start of the second half and enjoyed a good start in the early stages of the restart. They had a decent opportunity to reduce the arrears on 57 minutes when Cyrus Christie was found on the right by Downing and his cross was met by an unmarked Martin Braithwaite seven yards from goal. However, he got his header all wrong and the effort trickled weakly wide.

That prompted Monk to make his first change as the ineffective Jonny Howson made way for Rudy Gestede.

Boro were enjoying plenty of possession, but Millwall continued to look dangerous on the break and a sliding block from Ayala turned Gregory’s shot behind just after the hour mark.

Downing had switched from the right flank to a deeper role following the introduction of Gestede and was beginning to have more of a say in proceedings. So much so that he hauled Boro back into it out of nothing with a long-range drive in the 67th minute which slipped through the fingers of Jordan Archer.

Boro’s tails were up and Braithwaite’s fizzing cross was just a few inches in front of Assombalonga in the 73rd minute, but Millwall should have increased their lead on 78. Leadbitter’s poor header fell to Morison who sent a chipped cross towards the far stick. Tunnicliffe was waiting but mishit his shot and sent it rolling into the grateful arms of Randolph.

Boro made a double substitution soon after as Christie and Braithwaite were replaced by Adama Traore and Marvin Johnson. Monk urged his men to push further up the pitch but, with gaps at the back, it was almost 3-1 to Millwall when Morison went through but saw his shot saved by the outrushing Randolph.

Middlesbrough threw everyone bar Randolph forward in stoppage time and Ben Gibson saw optimistic appeals for a handball in the box waved away in the dying seconds as Monk’s men fell to another costly defeat.

For Millwall it was another win against a side in the top half of the table, following their 3-1 success against Sheffield United in their last home league game.

And manager Neil Harris is keen for his team to extend that run and turn the Den into a fortress this season as they stretched further away from a possible relegation battle.

He said: "Top teams don't particularly like coming here this season. We are what we are as a football club. We have to make it hostile, intimidating. We have to play aggressive football with and without the ball. We play very good football as well, you see that with the first goal in particular.

"We haven't got players that are worth millions of pounds, but I think I've got a lot of players growing in reputation at this level because they are very good footballers.

"The biggest credit I can give them is they are a very good team, as in together. I thought we made a top Middlesbrough side look really ordinary today at times.

"The only disappointment is that we didn't keep a clean sheet and we didn't go and score four or five. When the game became rough and tumble and aggressive and a fight, we shone and we dominated."