Diaz, halfway through a four-year, $8 million deal with St. Louis, was taken off the Cards' 40-man roster earlier this year. The 25-year-old hit .333/.404/.574 in his final 45 games last season, putting him in position to contend for a backup infielder role next year.
Kiekhefer went 2-1 with a 2.41 ERA in 50 games for Memphis last season, walking only seven batters in 59 2/3 innings. The 26-year-old, currently playing in the Arizona Fall League, could find a role as a lefty reliever for the Cards next year.
Tilson, 22, hit .295/.351/.388 with 46 stolen bases while primarily playing center field for Springfield last season.