Afterward, Diaz, who defected from Cuba in 2012 in order to establish residency in Mexico and pursue his dream of playing in the Major Leagues, spoke of the anticipation building toward this day.
"It was a very difficult process," said director of international operations Moises Rodriguez, who served as Diaz's translator. "It was a process that, at times, was very stressful on him. But it did allow him time to reflect on things he could improve on as a ballplayer. He also used the time to prepare because he knew this day would come and he wanted to be as ready as possible when that day got here."
Because of his defection and a subsequent suspension by Major League Baseball for falsifying a birth date on his documentation, Diaz has not been able to play in games for about a year and a half. There will be a delay before he gets in a Major League Spring Training game, too, as Diaz first must return to Mexico to obtain a work visa.
General manager John Mozeliak said the organization anticipates Diaz making that trip early next week.
In the meantime, Diaz is free to play in Minor League games as soon as the Cardinals clear him as game-ready. The Minor League spring schedule begins on Thursday.
"We looked at him, really, in a Cardinal uniform for the first time today," Mozeliak said. "We'll assess where he's at and then make that decision shortly. I think he's a real complete player. I think from an offensive standpoint, he always performed well when he was playing down in Cuba. How that translates to the states, time will tell, but we're very confident he could be an offensive middle infielder, specifically a shortstop."
Though Diaz has the versatility to play elsewhere in the infield, the Cardinals intend to use him exclusively at short. He will begin the season in the Minors -- where exactly has not been determined -- and Mozeliak cautioned patience as Diaz adjusts to a new level of competition.
This was not a signing made to impact the Major League club in the immediate. Rather, it was a move intended to improve the depth at a position where the Cardinals were thin.
"He hasn't played baseball in really over a year and a half competitively, so it's not something where we're looking to have him put his fingerprints on the Major League team tomorrow," Mozeliak said. "We can give him time to develop and from a talent standpoint take his time to get back to where he was. I think from our organizational standpoint, that's a great fit for us at this time."
Though Diaz began this process seeking an organization that had an opening for him in the big leagues right away, the Cardinals were open with him about their plans to first give him time in the Minors. Diaz nevertheless saw it as the right fit for him because the Cardinals "paid a lot of attention to [me] throughout the evaluation process."
Diaz added that he "likes the St. Louis fan base [and] knows there is a tradition there with the team and knows that they're going to appreciate his hard work when he goes on the field of play."
The evaluation process of Diaz was extensive for the Cardinals, who only recently poured more resources into scouting and evaluating players from emerging international markets like Cuba and Asia.
As the Cardinals sought to understand the Cuban market, they also had the challenge of trying to scout a player who was not playing in games. Diaz, who played in Cuba's top professional league from 2007-12, was able to showcase his tools at several workouts, including one at the club's Florida complex last month.
Rodriguez and director of player personnel Matt Slater did much of the background work on Diaz.
"Both Moises and Matt will tell you from a makeup standpoint, he really fits the culture of what we're trying to do," Mozeliak said. "From a baseball standpoint, we like the offensive upside. From the defensive standpoint, we think he can handle that position. So when you put it all together and then take a step back and look at the Cardinal organization, where he fits into our top prospects now is pretty high up there. And now we also have one that's a shortstop. From an organizational standpoint, we feel really good about that."
Though Diaz is not able to return to Cuba, he remains in contact with his family there. They are "all very supportive and extremely happy that this day has finally come," Diaz said. He has also been in touch with Leonys Martin, who came out of Cuba and signed with the Rangers in 2011. Martin has shared his experiences about assimilating into a new country and a new league.
"You can see he's a little overwhelmed," manager Mike Matheny said. "He's thrust right into a new culture, let alone a new team. But we all speak the common language of baseball around here, and hopefully this will be a very comfortable place for him to get things started."