Velez Sarsfield won their eighth Argentine title yesterday with a match to spare when they beat Huracan 2-0 away on the season's penultimate weekend
Second-placed Lanus bowed out of the race after their first home defeat of the Clausura championship, 1-0 to Argentinos Juniors, to fall four points behind Velez.
Uruguayan striker Santiago Silva headed Velez into the lead six minutes after halftime in a match played behind closed doors because of a ban on spectators at Huracan's Duco stadium after crowd trouble three weeks ago.
Substitute David Ramirez converted a late penalty for his eighth goal of the championship as Velez's top scorer after team mate Sebastian Dominguez and Huracan defender Facundo Quiroga were sent off in the 75th minute for fighting.
Argentinos scored their winner in the 57th minute when Gustavo Oberman's lob came back off the post to German Basualdo who squared the ball for striker Nicolas Blandi to fire home.
"We had a good championship overall but we lost at home for the first time, that's football," Lanus's former Italy midfielder Mauro Camoranesi told Futbol Para Todos.
Lanus were the form team of the last four weeks with four wins in a row and were unbeaten in 11 matches. Velez had mixed four wins with two defeats in their previous six games.
Earlier, River Plate drew 1-1 away to Estudiantes, Apertura title winners in the first half of the season, to remain at risk of dropping into the relegation-promotion playoffs if they lose at home to Lanus in their last match next weekend.
Right back Paulo Ferrari fired River into the lead early in the second half with a fine left-footed shot from outside the box but defender Matias Sarulyte headed the equaliser six minutes later from a Leandro Benitez free kick.
"We're going home angry because these matches are very hard to win and you have to take advantage when you take a lead," Ferrari told reporters.