Tony Adams was disappointed with Portsmouth's "schoolboy errors" in defence which proved costly as Fulham ran out 3-1 victors.
Pompey travelled to Fulham needing three points but things started badly when Andy Johnson found himself with just David James to beat, after some poor defending from captain Sylvain Distin, and the striker made no mistake in the 14th minute.
The away side had a chance to level before half-time when Younes Kaboul's header came back off the crossbar but the second half proved costly for Portsmouth as Fulham substitute Erik Nevland bagged a brace and embarrassed the away side's nervy defence.
Under-fire Adams had some consolation when striker David Nugent headed home with six minutes to go, but the former Arsenal captain knows the defensive errors were the difference between the two sides.
"I think we made too many mistakes today. We made some schoolboy errors defensively. To get anything out of the game when you make mistakes you don't win football games," Adams told Sky Sports.
"We worked all week, this week, about the way that Fulham play and their wide guys get in behind our central midfield players.
"I've worked with them on the training pitch and we've come to the match day and we've made the same mistakes, we need to put it right quickly."
With a dismal record of no wins in eight games, Adams is hopeful of bringing in new faces to shake up his side which appears to be lacking in confidence as they hover precariously above the relegation zone.
One player heavily linked to Fratton Park is Tottenham youngster Giovani Dos Santos. However Adams dodged naming transfer targets, saying: "I'd like in a couple more players and then I'll be relieved that this window actually finally shuts.
"Players' heads do get turned and it's difficult so I'll be pleased if we can get a couple of players in, that'd be great because I'm a little bit limited for options off the bench and personnel (with injuries)."
On the rest of the season, he added: "We have to keep working hard and believe and keep the faith and battle on. We've got a big game against Liverpool now and you try and get three points."