The result made it five goals conceded in the Blues' last three Premier League matches.
"You can't feel secure in football matches if you keep giving goals away," Lampard told BBC Sport afterwards.
"When you go 3-1 up, if you can navigate the next five minutes, the game should be more comfortable for you.
"But, straight away, we switch off and make two or three mistakes in the build-up to a goal. Not good enough."