MILLWALLL boss Neil Harris admitted his side are "far too easy to score against" after the 3-1 defeat to Southend ended their four-game unbeaten run in the league.
Dave Mooney gave the Shrimpers an early lead before Aiden O'Brien levelled with his fourth goal of the season to leave it 1-1 at the break.
Stephen McLaughlin made it 2-1 shortly after half-time when he volleyed home after Steve Morison had cleared a corner to the edge of the box before Luke O'Neill's close-range finish in the 87th minute helped seal Southend's first win at home in the league since March.
Millwall could have gone ahead in the second minute when Mahlon Romeo got a shot away in the box that Mark Oxley saved, but the goalkeeper was rarely worked after O'Brien's equaliser as Southend won just their second league game this season.
"I thought the first half was even, we started well and should have been in front," Harris said. "But they go down the other end and we're too easy to score against and it quickly turns into a real battle with tackles flying in and an aggressive nature to the game.
"They were very direct with their play and we matched it at times. We played a bit as well with some good quality to get into good areas.
"They went direct with some long throws and things like that and we had to stand strong. I was quite happy at half-time, barring the goal.
"In the second half we had to make good decisions whether to go long to Moro and pick up the second balls or play an extra pass. They played a direct game again and at times we didn't use the ball wisely."
Harris was forced into a defensive reshuffle five minutes before the break when he took off Joe Martin, who had been booked for a foul on Jermaine McGlashan before escaping a second yellow after he had caught Mooney late.
Harris admitted afterwards he replaced Martin with Lee Gregory as the defender was in danger of getting sent off.
The result meant Millwall dropped out of the top six to eighth place in the League One table, and they have now conceded 14 goals in eight games, the joint-second worst in the league behind Gillingham.
Eleven of those have been conceded away from home, and Harris spent a number of minutes poring over the defensive lapses at Roots Hall with video analyst Dan McLoone before he spoke to the waiting media.
The Lions boss admitted afterwards the defensive performances are an area of concern.
Harris said: "I'm really disappointed with the nature of the goals. I said to the guys as a unit, as a team, as a squad we have to get back to a clean-sheet mentality. At the moment we're far too easy to score against and the boys have to come into work every day with desire and hunger to want to be better.
"We've got a great group of lads, a great dressing room with a really good spirit and that needs to translate onto the pitch."