On 8 September 1968, Boca Juniors ended San Lorenzo's 26-game unbeaten streak, defeating the defending champions 0-1.
San Lorenzo's run started with the last two matches of the 1967 Nacional competition and extended throughout the entire 1968 Metropolitano campaign, which ended with them as champions--the first time in Argentina's history that a team won a national title without a loss (Racing came close in 1966, losing only a single game).
The last contest of the season, a 2-1 victory over Estudiantes in the league final, was their 26th consecutive game unbeaten, matching the streak by Boca Juniors in 1943-44. Coincidentally, San Lorenzo ended that run, beating Boca away, 2-1, so Boca took great pleasure in turning the tables on San Lorenzo with an away win of their own over the title holders in the first game of the 1968 Nacional.
At the time, the record unbeaten run in Argentina was 39, set by Racing from 1965 to 1966, but Boca Juniors went on to beat that in 1998-99, setting the current record at 40.