Published: 2019-10-10 04:43:54 BdST
The Germans, missing a dozen players and without a single world champion in the starting line-up for the first time since the 2014 World Cup final, fielded a callow team including newcomers Robin Koch and Luca Waldschmidt.
Gnabry turned provider seven minutes later when he found Kai Havertz in the box to complete a quick move.
Marcel Halstenberg rattled the crossbar with a stunning left-footed free kick as did Argentina's Rodrigo De Paul with a long-range effort.
The Germans, who had four players making their debuts, gradually ran out of steam and the visitors completed their comeback when Alario charged into the box to lay off for Ocampos to equalise.
Germany next take on Estonia in a Euro 2020 qualifier on Sunday.