He realized that there are a lot perks being a big leaguer. The one glaring thing he noticed is that the food in the clubhouse tastes much better than what he experienced in the Minor Leagues.
"You can see the difference in the big league level -- all the perks you get. The gifts are nice. They have a good buffet," Diaz said through an interpreter. "It makes you want to work harder to get [to the Major Leagues]."
Diaz, 21, has worked hard enough to have his best season in professional baseball. He is hitting is .297 with six home runs and 28 RBIs for Potomac, the Nationals' Class A affiliate.
A Nationals player who got to see Diaz play recently was second baseman Jose Vidro, who played with the outfielder for a week at Potomac during a rehab assignment. And, according to Diaz, Vidro told him that he had the potential to be a big leaguer one day.
"Vidro worked a lot with me," Diaz said. "When he was called up to the big leagues, Vidro talked to [Nationals manager] Frank Robinson and said, 'We got to get this guy to the big leagues.'"
The right-handed Diaz is at least two to three years away from playing in the Major Leagues. In fact, according to director of player development Adam Wogan, the plan is for Diaz to stay at Potomac for the rest of the season. Diaz has never hit above .277 before this season and he is considered an average outfielder.
But after working with Nationals hitting coordinator Mitchell Page during Spring Training, Diaz believes he can someday put up numbers like first baseman Albert Pujols, who worked with Page when both were with the Cardinals from 2001-04.
Page taught Diaz to have a shorter path to the ball. Page wanted Diaz to bend his back leg, keep his front leg straight and have his hands closer to the plate. During his follow through, Diaz swings with one hand. Diaz's stance and swing is similar to former Rangers and Royals catcher Don Slaught.
"The new approach had helped me a lot," Diaz said. "That's why I'm hitting close to .300. Even if I struggle, I'm going to stay with this approach."
One thing that Diaz doesn't have yet is Pujols' patience at the plate. While he doesn't strike out a lot, Diaz is known to swing at a lot of pitches. And Sunday's game was proof of how impatient Diaz can be.
He entered the game as a pinch-hitter in the fifth inning and struck out on three pitches against right-handed Cardinals prospect Chris Lambert. Diaz swung at all three pitches, none of which were in the strike zone.
Diaz would later get a second at-bat and strikeout swinging.
"He's a plus-guy that will hit for a high average," Page said on Sunday. "If he stays on the hitting program that we have set up for him this winter, he will be even better."
Diaz also had to make adjustments in the outfield, making the switch from right to center field. Diaz said the Nationals told him to play the position because it would help him get to the big leagues quicker.
Diaz doesn't have great range in center, but he is not considered a liability at the position.
"He was kind of imitating Andruw Jones with the laid back catch, but he gets the job done," said Nationals scouting director Dana Brown. "We like him. He has the chance to be an everyday center fielder. He is really a prospect with the bat."
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.