Masterson, acquired in a trade with Cleveland on July 30, allowed three hits _ all singles _ and no walks and threw only 91 pitches before departing for a pinch hitter.
After recording only six outs in his previous start, he lowered his ERA to 6.00 in three outings with the Cardinals, and 5.14 overall this year.
The 6-foot-6 right-hander improved to 2-1 with St. Louis and 5-6 overall. He also earned his first career RBI in the sixth with a two-out single.
Nathan Eovaldi allowed four runs, two earned, in six innings.