Immobile sent the keeper the wrong way after Nikola Milenkovic was penalized for a handball four minutes into stoppage time.
Both sides found chances hard to come by but it was Fiorentina which came closest early on. Lucas Beltran had an early goal chalked off after a video review and then hit the post with a header.
The result meant Lazio moved up to seventh spot, a point and a place behind its opponent.
Gianluca Scamacca scored twice and laid on another for Atalanta.
Scamacca put the visitors ahead with the cheekiest of goals just five minutes into the match, taking an Ademola Lookman pass and backheeling it through the legs of the advancing goalkeeper.
Scamacca capped a dominant performance when he added a third six minutes into the second half.
Empoli remained third from bottom.
AP soccer: https://apnews.com/hub/Soccer
The Associated Press