Lazio beats Frosinone to be a point behind 4th-place Milan
The top four in Serie A qualify for the Champions League.
Lazio's victory was far from convincing. It took the lead in the first half when Luis Alberto threaded the ball through to Felipe Caicedo and he took one touch before striking it powerfully into the back of the net.
There had been controversy 10 minutes earlier when referee Michael Fabbri awarded a penalty to Frosinone for a presumed tug from Bastos on Camillo Ciano but he revoked his decision on video review.
Frosinone remained second-to-last, five points from safety.
Atalanta almost conceded a stoppage-time equalizer to dent its Champions League aspirations.
Alessandro Deiola's flicked header from a corner beat Atalanta goalkeeper Etrit Berisha but bounced off the crossbar much to the visitors' relief.
Hans Hateboer headed in Timothy Castagne's deflected cross for the only goal, five minutes into the second half.
Cyril Thereau, who is on loan from Fiorentina, had a miserable debut for Cagliari as the forward limped off with a muscular problem 20 minutes after coming off the bench.
Cagliari was four points above the relegation zone.