Immobile struck his 35th league goal of the campaign eight minutes from time in Rome to close in on Gonzalo Higuain’s record of 36 goals, scored for Napoli in 2015-16.
With one game to play Lazio are fourth, equal on 78 points with third-placed Atalanta, who beat Parma 2-1 on Tuesday, and one adrift Inter Milan who are second following their 2-0 win over Napoli.
All three teams are targeting second place behind Juventus, who sealed a ninth consecutive Serie A title at the weekend.
Inter and Atalanta will go head-to-head this weekend with Lazio’s last game at seventh-placed Napoli.
Immobile helped Joaquin Correa open the scoring after 16 minutes at the Stadio Olimpico, with Correa returning the favour late on.
Juventus star Cristiano Ronaldo is four goals behind Immobile as the champions take on Cagliari later Wednesday.
Behind the top four, who are assured of Champions League football next season, AC Milan kept the pressure on fifth-placed Roma for the Europa League group stage berth.
Zlatan Ibrahimovic scored twice and set up a third as Milan beat Sampdoria 4-1, leaving Stefano Pioli’s side one point behind Roma, who play Torino later on Wednesday.
The 38-year-old Swede got his head to an Ante Rebic cross within four minutes in Genoa for his fastest goal in the Italian top flight.
Ibrahimovic then nodded the ball across for Hakan Calhanoglu to add the second six minutes after the break.
Turkish winger Calhanoglu provided the cross which allowed Ibrahimovic to add his second of the night.
Leao added a fourth in injury time as Milan extended their unbeaten run to 11 games.
Ibrahimovic has scored nine league goals since rejoining Milan in January.
The veteran brings his club tally to 51 goals for the club, combined with his previous stint between 2010 and 2012.
He also becomes the first player to have scored 50 goals for both Milan clubs, with 57 netted during his time at city rivals Inter from 2006 to 2009.
Lecce’s bid for survival will go down to the final day after they came from behind to beat Udinese 2-1.
The southern club occupy the final relegation position but are now just one point behind 17th-placed Genoa, who were hammered 5-0 at Sassuolo.
Both Lecce and Genoa will face Parma and Hellas Verona respectively at the weekend to avoid joining Brescia and SPAL in Serie B next season.
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