Favourites Boca Juniors failed to break down nine-man Racing Club in a 0-0 draw at the Bombonera on Sunday but kept the eight-point lead that should guarantee them the Argentine title with four matches to go.
After 15 matches, unbeaten Boca have 33 points and Racing 25 with four teams a point further back including title holders Velez Sarsfield and Colon, who beat Atletico Rafaela 1-0 in Santa Fe with a goal from veteran striker Esteban Fuertes.
Lanus, who have 23 points, can move up to second within seven of Boca if they beat Arsenal at home on Monday.
Racing needed to win on Sunday to keep a realistic chance of beating Boca to the Apertura championship crown.
Instead, they would have lost but for some fine goalkeeping from Sebastian Saja, who kept Racing afloat as midfielder Agustin Pelletieri was sent off in the 49th minute for a second booking and Colombian striker Teofilo Gutierrez was shown a straight red in the 76th.
Gutierrez, who controversially arrived back late on Friday from international duty with Colombia on Tuesday, attacked referee Nestor Pitana after believing he should have been awarded a penalty when he went down in the box.
"It's really depressing. We needed to win [to stay in the title race] but to beat Boca is hard enough, no-one has done it with 11 men so to do so with nine is practically impossible," Saja told reporters.
San Lorenzo, another of Argentina's "Big Five" clubs, were beaten 1-0 at home by promoted Union and remain stuck in the bottom four places of the relegation table.
Relegation is calculated on points averages over three seasons and, as things stand, the Saints will need a play-off at the end of the season in June to try to retain their first division status.
Playmaker Paulo Rosales scored the only goal against the run of play when he spotted goalkeeper Nereo Champagne off his line and lobbed into the net from outside the box in the 73rd minute.
The home players were jeered off the Nuevo Gasometro pitch by their fans, who accused them of a lack of passion and demanding more commitment.
Central defender Jonathan Bottinelli, one of the principal targets of the fans' ire, said: "We played a great game but suffered a fatality as has been happening to us lately. We made one mistake and they scored."
He told reporters he was against coach Omar Asad quitting because he did not think that would resolve matters, adding "We have to grit our teeth and bear it."comments