The Vipers competed in the A-League, the second level of American professional soccer at the time, behind Major League Soccer, but played their home games at Tottenville High School and Wagner College. Osorio devoured the opportunity.

“He took his job very serious and was always trying to better himself so he could better the people around him,” Gaitan said. “He was also one of the most competitive people you can be around. He had a great ability to relate to players, and I believe that being a former player helped him a lot.”

When the Vipers folded in 1999, Osorio contacted the MetroStars in M.L.S.

“Juan Carlos knocked on my door looking for an opportunity,” said Octavio Zambrano, then the team’s coach. “I was looking for a bilingual trainer with experience. He was respectful and had the acumen to become a good assistant, but I needed to see his personality and ability to deal with professional players.”

So Zambrano took Osorio on the MetroStars’ preseason tour of Spain and Portugal to evaluate him.

“The players took an immediate liking to him because of his preparation for every session and his individual care for each one of them,” said Zambrano, now the director of youth development for Club Deportivo El Nacional in Ecuador. “By the time we got back to New York, he had earned his position.”

The traits refined during those early years set Osorio on a path toward four club championships and two domestic cups as a head coach — and defined a meticulous, intellectual, collective approach that has helped Mexico win or tie 21 successive games.