San Lorenzo soon became one of the top clubs in Buenos Aires; ever since the start of professionalism in 1931, it was counted in the top five (cinco grandes) together with Boca Juniors, River Plate, Racing and Independiente.
In the 1930s, Isidro Lángara and other players of Basque descent endeared San Lorenzo to the Basque community. The team also relied on players from the provinces, known as los gauchos, and won its first professional title in 1933.
In 1946, San Lorenzo broke the River Plate monopoly and won the league title; the team then went on to a tour of Spain and Portugal that was one of the highlights of the club's history. After losing to Real Madrid, it went on to defeat Barcelona and both the Spanish and Portuguese national teams; the Spanish press acclaimed San Lorenzo as "the best team in the world". Player René Pontoni was offered a contract with Barcelona but declined to leave Argentina (Barcelona then drafted River Plate's Alfredo Di Stéfano). Fellow player Reinaldo Martino did stay in European football and would later become a star with Juventus.
In the 1960s, a generation of players known as carasucias (literally: dirty faces) were the darling of Argentine fans because of their offensive, careless playing and their bad-boy antics outside the pitch. The 1968 team was nicknamed los matadores as it won the championship without losing a single game. In the years 1968-1974 San Lorenzo won a total of four league titles, its best harvest ever.
Unfortunately, poor administrations led San Lorenzo to a huge economic crisis, that even forced it to sell their well located stadium. The team was relegated in 1981, only to return to the top division with great fanfare in the 1982 season, which set all-time attendance records for the club.
By that time, the club had no stadium and was plagued by debt and irregularities. Controversial president Fernando Miele (1986-2001) delivered both the new stadium and two league titles: the Clausura '95 (after 21 years without winning a first division title) and the Clausura 2001 (in which the team achieved 11 consecutive victories). In late 2001 Alberto Guil was elected as president, and a month later San Lorenzo achieved its first international title: the Copa Mercosur 2001. San Lorenzo also won the first edition of the Copa Sudamericana in December 2002. The current president is Rafael Savino, and the club finances are running a deficit of near half a million dollars per month.
San Lorenzo is identified with the working class atmosphere of the Boedo neighborhood. Its derby rival from the southern part of Buenos Aires is Huracán, which was promoted back to the first division for the 2007/08 season.
The old Estadio Gasómetro stadium in Boedo was a venue of great renown, where many international games were held. Due to debts, it was sold in 1979 and torn down. The new stadium, called the Nuevo Gasómetro was opened December 1993 in the intersection of the Perito Moreno and Varela avenues in the Flores, Buenos Aires neighborhood.
The official name of the stadium is Estadio Pedro Bidegain after a former club president. It has a capacity of 43,494 and the pitch size is 110 x 70 m.