Coach Ian Chandler admits Portsmouth are in a London one south relegation fight after his side slipped to a 28-25 defeat against Hove at Rugby Camp.
The city club are fourth from bottom, just four points above Trojans who increased the pressure by winning at the weekend.
It was a frustrating afternoon for Chandler, who watched his side dominate much of the contest only to lose it at the death.
‘We are in a relegation fight and if we don’t recognise it, we’ll be in big trouble,’ he said.
‘Some of the rugby we played was our best this season, with forwards and backs linking superbly.
‘We raced into a 17-0 lead with the wind behind us in the opening stages of the first half but then failed to add to our score in the final 20 minutes of the half.
‘That was the deciding factor and what cost us.
‘All of a sudden a bit of complacency crept into our game and we started making some wrong decisions.
‘Players started to go on their own and we lacked composure when it counted.’
Portsmouth scored a superb team try in the opening minutes with Tom Hankey crossing the line after seven phases of controlled rugby.
Andy Barnes added the conversion and did so again after Portsmouth were awarded a penalty try at a scrum close to the line.
Another Barnes penalty saw Portsmouth cruising at 17-0 but they missed other opportunities to extend their lead before the break.
Although Hove hit back with a close-range try at the start of the second half, Portsmouth kept to their game plan of keeping the play tight to strangle Hove.
The visitors were put under sustained pressure which led to them having a player sin-binned.
Portsmouth made the error of expanding their game at that stage and it cost them.
Mistakes led to two Hove tries and, although Rich Farmer added a third try for the hosts, a drop goal and a penalty saw the two teams deadlocked at 25-25 in the final minute.
There was heartbreak for Chandler when his side conceded the winning penalty in the final play of the game.
‘We never controlled the game when it needed to be controlled,’ he said.
‘It is vital that we make it count when we are on top in games
‘This was a harsh lesson for us to learn.
‘We only made four mistakes all game.
‘And they made us pay dearly for them.
‘Our forwards were totally dominant and we played really well for most of the game.’