Lanus won the Argentine championship for the first time in their 92-history on Sunday, sealing the title with a 1-1 draw at Boca Juniors.
Tigre, the only team with a chance of catching them, suffered a 1-0 defeat at Argentinos Juniors.
Lanus finished the campaign with 38 points from 19 games, four ahead of Tigre and another three clear of third-placed Boca.
Needing only a draw from their final match, Lanus went ahead eight minutes before half-time when striker Jose Sandheaded home at a corner to record his 15th goal of the campaign.
Boca equalised midway through the second half when striker Martin Palermo scored at the second attempt after his first effort was saved by Mauro Bossio.
Three minutes later, Boca had Colombian midfielder Fabian Vargas sent off for a rash tackle on Sebastian Blanco.