The England midfielder has also warned the Blues to forget about playing in next season's Champions League unless they up their game in the closing stages of this Premier League campaign.
Lampard said Chelsea had let their standards slip since they came back to knock Napoli out of the Champions League a fortnight ago -- a result that set up Tuesday's quarter-final first leg away to Portuguese giants Benfica in Lisbon.
Chelsea sacked manager Andre Villas-Boas in between the two legs of their tie with Napoli and promoted his assistant Roberto Di Matteo, the former Blues midfielder, to caretaker coach.
Since beating Napoli at Stamford Bridge, the west London club have reached the FA Cup semi-finals but have taken just one point from two Premier League games and are now five points adrift of fourth-placed Tottenham Hotspur after a goalless draw with Harry Redknapp's side on Saturday.
"The fixtures and where we are in the table doesn't lie -- we're not as good as we used to be," Lampard told Chelsea TV.
"We used to have a fortress here and, for whatever reason, we're just not doing it. It's something we must all put right.
"You know a derby against a very good Tottenham side is going to be tough. But I don't think we were at it enough. We had to play more with the urgency we showed against Napoli.
"Against Tottenham, we didn't really do enough to lift the fans. We had the high of Napoli, then we got beaten by Manchester City and now we need to up it again."
Chelsea have finished in the top four for nine successive seasons and Lampard said: "Chelsea should be in the top four. No disrespect to the other top-five clubs but, with the ability we have, we should be in there.
"It is far from over. There is no point being downbeat about it at the minute. It's five points and the gap has been bigger than that. It's up to us now to get ourselves right for Benfica and the league games coming up."
But Lampard said it would take a huge effort to overhaul Tottenham and finish fourth.
"That's due to dropping points throughout the season, not drawing with Tottenham at home," he insisted.
"It's losing games we should have won home and away. We have to take all the league games now as knockout matches.
"It's very cliched but we're fighting from behind, and if we lose a game and lose points then the gap is bigger and the amount of games left is shorter.
"So we know, especially after that draw, the gap is still five points and there is no more room for slip-ups."
Source: AFP
Source: AFP