Boca Juniors' hopes of retaining the title hang in the balance after their shock 3-0 home defeat by Arsenal and the Libertadores Cup semi-finallists need a win at All Boys next Sunday to have any chance of overhauling the leaders.
Arsenal joined Tigre, 1-0 winners away to Velez Sarsfield on Saturday, on 35 points at the top of the standings, two points ahead of Boca with one round of matches to go.
Emilio Zelaya stunned the packed Bombonera by heading Arsenal into the lead in the second minute from Colombian winger Carlos Carbonero's cross and fellow striker Luciano Leguizamon added two more goals either side of halftime.
Angry Boca fans threw objects at the match officials as they came off at halftime with one hitting linesman Sergio Viola in the face.
Boca coach Julio Cesar Falcioni, whose side are also chasing the Libertadores Cup and Copa Argentina, was sent to the stands for dissent at half-time and defender Franco Sosa was shown the red card six minutes from the end for elbowing an opponent.
If two or three of the trio of teams still in the race finish equal on points next Sunday, the title will be decided by playoffs as goal difference is not taken into account.
"We must work on the squad's recovery to try to reach the [Libertadores Cup] final," said Falcioni. His team visit Universidad de Chile on Thursday leading 2-0 from the first leg of their semi-final.
"We're feeling the strain of the semester but we're in the final straight and have to make a maximum effort," he told reporters.
All Boys, five points adrift of the leaders, had four players sent off, three with direct red cards, in a chaotic match at Argentinos' Diego Armando Maradona stadium.
Referee Saul Laverni began what the sports daily Ole called "the card show" by sending off defender Jonathan Ferrari in the 16th minute.
After a player from each side had been sent off early in the second half, midfielder Juan Jose Morales scored the only goal in the 73rd minute.
Morales was the next player sent off. He was booked for taking his shirt off to celebrate his goal by showing a "happy father's day" message to his dad and he earned a second yellow card for a tackle from behind two minutes later.
All Boys had two more players sent off in the last nine minutes.
Newell's Old Boys, beaten 2-1 at lowly San Martin on Friday, and Velez Sarsfield, Clausura champions a year ago, also fell out of the title race.
Estudiantes fans gave Juan Sebastian Veron a rousing farewell in his last home match before retirement. Estudiantes are away to Union next weekend in the 37-year-old Veron's last match.
A colourful occasion at a packed Ciudad de La Plata stadium on Saturday was marred only by a very poor match settled at a corner delivered by Veron and headed home by defender Gabriel Mercado for a 1-0 victory over Olimpo.
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