The modest club from the suburb of Sarandi, founded in 1957 by present Argentine Football Association president Julio Grondona and his brother, finished the 19-match championship with 38 points, two more than their closest challengers Tigre, who were held 2-2 at home by Independiente.
"This is a huge happiness, something fabulous," Arsenal club president, Grondona's son Julito, told reporters. "The smallest [first division] club in Argentina were champions, the one with the fewest followers."
Tigre, who began the day equal on points with Arsenal at the top, went ahead in the 20th minute with striker Carlos Luna's 12th goal confirming him as the tournament's top scorer.
However, a brace from playmaker Patricio Rodriguez early in the second half put Independiente ahead before a late equaliser by Diego Morales with a penalty after the visitors' Osmar Ferreyra had been sent off.
Tigre's point was enough to save them from a play-off with a team from the Primera B Nacional (second division) for their top flight survival. While vying for the championship, Tigre were dangerously low in the relegation standings, a separate table based on team's average points over the last three seasons.
Boca, who had effectively kissed the title goodbye in an upset 3-0 home defeat by Arsenal last weekend, fielded reserves at All Boys as the first team were rested for the first leg of South America's Libertadores Cup final at home to Corinthians of Brazil on Wednesday.
Colon's 39-year-old striker Esteban Fuertes marked the last match of his career with two goals for a championship tally of seven.
San Lorenzo's 3-1 home win over San Martin with two goals from their Uruguayan striker Carlos Bueno put them into a promotion-relegation play-off with Instituto, who finished third in the Primera B Nacional.
