Surprise team Huracan beat Arsenal 3-0 at home on Sunday to set up an Argentine Clausura championship decider against Velez Sarsfield next weekend.
Big guns River Plate and Boca Juniors both lost, Boca 2-1 at home to Gimnasia-La Plata under reserves coach Abel Alves before the expected return next week of Alfio Basile following the sacking of Carlos Ischia.
Huracan snatched the lead in the standings by one point from Velez, who were held 1-1 at Lanus, the other team who began the day with a chance of lifting the title but have dropped out of the picture.
Arsenal were a man short for more than an hour after midfielder Cristian Pellerano was sent off for a second booking and striker Mario Bolatti headed Huracan in front shortly before halftime.
Two goals in the final nine minutes sealed the win. Patricio Toranzo shot into the roof of the net from Javier Pastore's low left cross and less than two minutes later Matias Defederico, who recently won his first Argentina cap, raced between two defenders to steer home the third.
A draw at Velez will be enough for the title to go to Huracan, a modest club who have had little to cheer about since Cesar Luis Menotti steered them to their only championship in 1973 before taking charge of Argentina and leading them to World Cup victory in 1978.
Velez, looking for their sixth league title and first since 2005, have the credentials to spoil Huracan's ambitions with the best defence and only one defeat in 18 matches.
They fell behind at Lanus to a goal by Jose Sand and had midfielder Fabian Cubero sent off in the 48th minute but equalised with a 69th-minute penalty by Uruguayan striker Rodrigo Lopez.
Huracan, who have suffered relegation since their glory days but can boast the great Alfredo di Stefano among their former players, are coached by Angel Cappa, a Spain-based Argentine who espouses the same attacking ideals as Menotti.
His young team have reduced older fans to tears with their spontaneous style and goals that have made them the most prolific team of the championship.
At Boca's Bombonera (Chocolate Box) stadium, Gimnasia took a surpise lead after only three minutes with a headed goal by Uruguayan forward Diego Alonso.
Boca equalised with a penalty by veteran striker Martin Palermo close to halftime but Gimnasia snatched victory with defender Ariel Aguero's header in the 54th minute.
Boca, defending champions having won the Apertura tournament in December, have 19 points, half the number of Huracan.
Sixth-placed River's 1-0 loss at Godoy Cruz to a ninth-minute goal by Ivan Borghello helped the home side stay clear of the relegation positions.