When the youngster turned around, Lopez saw "Mejia" on the back of his jersey and thought of Carlo Mejia, a shortstop Lopez played against in high school and college.
The boy, Alex, was Carlo's son.
"I said, 'If you're anything like your father, we're going to start recruiting you and get you to Tucson," Lopez recalled.
Lopez got Mejia to Tucson, and now the junior shortstop -- and the Cardinals' fourth-round pick in the 2012 First-Year Player Draft -- is part an impressive left side of the infield that has the Wildcats one win away from an NCAA championship.
Arizona (47-17) faces South Carolina (49-19) at 8 p.m. ET on Monday at TD Ameritrade Park in Game 2 of the best-of-three finals of the College World Series. The Wildcats won the Game 1, 5-1, on Sunday.
"He really is just like his father," Lopez said. "He plays hard, he communicates -- he just does all the things you want a baseball player to do. Three times [in Arizona's opener against Florida State] I got to the top step and he was on the mound, so I sat down. He's a joy to be around."
Mejia is one part of a loaded Wildcats lineup that is hitting .331 on the season and averaging 5.5 runs per game in Omaha.
Mejia's partner on the left side of the infield, third baseman Seth Mejias-Brean -- the Reds' eighth-round Draft pick -- is hitting .359 with 19 doubles and four triples. Mejia called Mejias-Brean a "phenomenal worker," and said Mejia doesn't have to worry about anything to his right when he's at shortstop.
"He's the best third baseman, in my opinion, in the nation," Mejia said. "I haven't seen anybody better play the position as good as he has."
Like Mejias-Brean, Mejia also is the complete package. The shortstop, who is hitting .358 with 12 doubles and six triples, earned Pac-12 Player of the Year and Pac-12 Defensive Player of the Year honors.
But numbers are only part of what makes Mejia the Wildcats' leader.
"One thing that really sticks out with me is just how he communicates really well with the whole defense," said Mejias-Brean, who has played next to Mejia for three years. "Talking to the pitchers, he's really the leader out there -- our captain of the infield -- and he's just a great player."
That leadership no doubt stems from Mejia's parents, Carlo and Norma, who were in Omaha for the Wildcats' first game.
The family, which lives in Sylmar, Calif., wasn't planning on coming until family members raised about $1,600 for the trip. Carlo's sister and brother-in-law presented him with an envelope full of money two days before Arizona's first College World Series game.
Unfortunately, Mejia's parents had to leave after the first game and won't watch him play for a title Monday. But they were still able to watch their son in Omaha.
"That's pretty sweet, man, it makes it worth while," Lopez said. "How many times are you going to see your son play in the College World Series? And have him play well and have his team play well?
"You go through a lot of headaches over the course of the year, and that kind of washes them all away."
So, too, would an NCAA title, which Lopez, Mejia and Mejias-Brean are one win away from achieving.
College World Series finals results and schedule
Sunday: Arizona 5, No. 8 South Carolina 1
Monday: Arizona vs. No. 8 South Carolina, 8 p.m.
Tuesday: No. 8 South Carolina vs. Arizona, 8 p.m. (if necessary)