Diaz was in the starting lineup to hit eighth. Washington started Gio Gonzalez.
Diaz last played in Cuba in 2012, then defected. His probably will start the season at Double-A Springfield.
''We need to get him exposed to this, and we are running out of time,'' St. Louis manager Mike Matheny said.
Diaz agreed March 9 to an $8 million, four-year contract that includes a $2 million signing bonus and salaries of $500,000 this year, $1.5 million in 2015 and $2 million in each of the final two seasons.
He worked out with the Cardinals last week and played in minor league exhibition games before going to Mexico for his U.S. work visa, which is needed before he can play in big league spring training games.
''We know there are going to be gaps, we just need to see where they are and how we can help him fast-forward through some of the stumbles,'' Matheny said.
Diaz was the second significant shortstop signing by St. Louis during the offseason following a $53 million, four-year contract with free agent Jhonny Peralta.