Fulham slipped to the foot of the Premier League table after a second-half capitulation that saw Southampton ease to their first victory at Craven Cottage for over 66 years.
Adam Lallana opened the scoring for the visitors with 64 minutes gone, before Rickie Lambert and Jay Rodriguez added further goals to condemn Fulham to a 17th league defeat of the season.
Cardiff City's 2-1 win over Norwich City moved the Welsh side ahead of the London club, who are now three points adrift of safety, and Fulham coach Meulensteen was quick to criticise his players.
"It typifies a little bit the last couple of games," Meulensteen told Sky Sports. "We've had really good first-half performances where we should get in front.
"Then a sort of fluky clearance from them, we're out of position, a good finish from Lallana and it's in the back of the net.
"The problem is that after that we conceded two more goals in 10 minutes and that is, at Premier League level, unacceptable.
"I didn't think we played well enough going forward to turn them and to create chances for ourselves. Especially at home, that is what you should be able to do."
Meulensteen admitted that Fulham's league position accurately reflects their displays this season, but knows there is plenty of time to turn things around.
"You have to be realistic and you have to not hide from the fact that you are where you are," Meulensteen added. "You are there for a reason because you haven't scored enough goals and you have conceded too many.
"We keep working ever so hard on it on the training pitch and in this transfer window we have changed a few things around.
"Hopefully a few more faces will lift the place because that's what we need to do, keep lifting ourselves and keep reminding ourselves that there is still a lot of games to play for."
