
Second-placed Lazio are 13 points adrift of leaders Napoli and increased their lead over AS Roma in third to eight points.
Lazio opened the scoring in the 36th minute with a coolly-taken spot-kick by Immobile, who sent Bartlomiej Dragowski the wrong way after a foul on Anderson in the box by Ethan Ampadu.
Maurizio Sarri’s men doubled their advantage seven minutes into the second half through a low shot by Anderson.
Antonio wrapped up a comfortable win in the 89th with his first goal for Lazio less than 10 minutes after coming on.
Spezia finished with 10 men after defender Ampadu got a second yellow for fouling winger Mattia Zaccagni six minutes from time.
Spezia, who are in 17th place on 26 points remain four points above the relegation zone.