Portsmouth crashed to a 36-31 defeat at the hands of Beckenham at Rugby Camp as their London one south survival hopes were rocked.
The city club proved their own worst enemy again.
Their failure to make tackles in the first half put them on the back foot and they were unable to recover.
Veteran winger Matt Gronow was controversially denied a try on the stroke of half-time by the visitors’ touch-judge.
But coach Ian Chandler refused to use that as an excuse.
The defeat leaves Portsmouth in the relegation zone with just three games remaining.
‘The players had a fancy dress evening planned and in the first half they defended like it,’ said Chandler.
‘We missed 20 tackles in the first half and you cannot defend like that and expect to win matches.
‘They were all tackles that should have been made.
‘In typical Portsmouth fashion we started well, were totally dominant but then took our foot off the pedal.
‘Good teams keep teams under pressure and are relentless in that situation.
‘We have the second worst defensive record in the league and that tells the story.
‘If we hadn’t had what looked a perfectly good try disallowed before the break it would have brought us back level but that wasn’t why we lost.
‘We just didn’t tackle.’
Portsmouth took charge at the start, racing into a 10-0 lead through an Andy Barnes penalty and a converted try by 37-year-old Gronow.
Three Beckenham tries before half-time, though, altered the complexion of the contest.
And after the touch judge decided Gronow put his foot in touch when going over the try-line Portsmouth found themselves trailing 17-10 at the break.
The home side allowed that incident to get to them and the visitors added a converted try at the start of the second period. Gronow took his anger out on the Beckenham defence with a superb score soon afterwards, leaving three defenders for dead with his pace before side stepping his way past four others for a try.
‘It was the best try I have seen him score and I have been watching him for over 15 years,’ said Chandler.
Portsmouth, however, conceded another two tries through poor organisation at restarts.
Replacement Nick Lynch did go over for a home try, though.
Then from the last play of the game scrum half Charlie Cutler salvaged two bonus points with a try, giving them some consolation.
‘If we defend like we did in the first half in our final three games I don’t hold out much hope for us,’ said Chandler.
‘There were lots of good individual performances but we were poor as a team.
‘It is criminal to relax after getting ourselves into a good position.’