TAMPA — People filed into the ceremony room at the U.S. Citizenship and Immigration Services office on Monday afternoon, some wearing red, white and blue ties, others showing off socks emblazoned with stars and stripes.Off to the side, Juan Mercado took a seat, placing his St. Louis Cardinals ball cap on a chair near him to save space for his parents.Fifty-one immigrants from 25 countries took an oath of allegiance and officially became U.S. citizens. Among them was Juan's brother, Oscar Mercado, who came to the United States from Cartagena, Colombia, with his family as a 7-year-old, thanks to his father's work visa.Since then, Oscar Mercado has made the most of the opportunity his family's move afforded him, finding success as a shortstop at Gaither High School before being selected 57th overall by the Cardinals in the 2013 Major League Baseball draft.After a couple seasons of frequent throwing errors and growing pains, it hasn't always been easy for Mercado. But then again, fulfilling a dream rarely is."America is a country where dreams come true," immigration officer Yireyma Lopez said to the crowd. "I'm sure everyone in this room has a dream. Some might be small, some might be big. But we all have them."In the first row, Oscar grinned, a small American flag clutched in his hand.• • •Oscar Mercado Sr. played soccer in his home country. But at night, the family of five would gather around the television for American broadcasts of Major League Baseball. When the San Diego Padres took on the New York Yankees in the 1998 World Series, Oscar Sr. couldn't get his 4-year-old son to look away.The family immigrated to the United States in 2002 and settled in Tampa. Oscar Sr. got his sons, still enchanted by the game, involved in the South Brandon Little League."Juan was 10 and Oscar was 8," Oscar Sr. recalled. "They said, '(Juan) will play this level, and (Oscar) will play at another level.' I said, 'No.' "Because the family only had one car, Mercado, who works as a general contractor, didn't have time to cart his children to different practices, so he talked them into allowing his youngest son to play an age group up, for convenience sake.On the diamond, Oscar has been standing out ever since.By the time he got to Gaither, he had polished his skills. He had an arm like few others longtime coach Frank Permuy had ever seen and the speed to match. As a junior, he hit .370 and drove in a team-high 29 runs. Still, driven by the opportunity his parents sacrificed to give him, Oscar didn't rest.While at Gaither, Oscar Mercado impressed coaches not only with his skill, but his work ethic. (Times file, 2010)."That's one thing that set him apart from everybody else, was his drive," Permuy said. "He was always wanting to go out and do extra work. When someone else wanted to stay late and do extra work, he'd stay out there with him."When Oscar got to the minor leagues, he began to draw attention for a different reason.The top-ranked shortstop out of high school in 2013, he committed 119 errors at the position through his first four seasons with the Cardinals' farm teams.Before the 2017 season, one in which he spent the entirety with the Double-A Springfield (Mo.) Cardinals, his coaches sat him down and talked to him about a move to the outfield."He texted me and said, 'I don't know how to tell mom and dad that this change is coming.' He never played in the outfield, not even in high school," his brother said. "It was kind of a shock when it happened, but a year removed, he's so good at it. I'm like, 'This has been your calling the whole time.' "• • •When the newest bunch of citizens stood to recite the oath, Oscar's mother, Marta — who, along with the rest of her family, became naturalized in 2016 — walked up to the front of the room to catch the moment on her iPhone.Afterward, Oscar was asked to share a few words at the podium.This year, Oscar, 23, is spending his first spring training with the big-league club, and he had a flight to catch back to the team's complex later that day. But when the ceremony concluded, he was the last one to leave.He posed for pictures with immigration officers, asking about the U.S. passport application process between snaps of the camera. Oscar then sat down with a representative from the board of elections. He registered to vote, and she rewarded him with a sticker for his jacket lapel."I guess I won't give you the spiel about working for us on election day," she said with a chuckle.On his way out the door, he stood in front of a replica of the Statue of Liberty, and, flanked by his family, took one last photo.Since receiving his $1.5 million signing bonus, Permuy said Oscar has helped his parents pay off their house and given his siblings, including twin Nathalia, money for their education (one is studying to become a CPA, and the other is applying for dental school).For Oscar, the last in his family to take the oath, Monday wasn't just about celebrating his American dream."The biggest thing is how many doors open up for you in this country. There are so many opportunities, not just in sports, but in everything.That's what my parents wanted for us," he said. "We all chose different paths, but we're all pursuing our dreams in our own way."