"He can give you a bunch of innings," Johnson said. "He's been a big part of the winning effort here."
Stammen entered Tuesday night's game with a 2-1 record and 3.38 ERA. He had already pitched in seven of the team's 19 games and was very strong in his last three appearances.
Stammen struck out seven in 5 2/3 innings over those three games. In Monday's game, Stammen threw a pair of scoreless innings and got out of a major jam in the sixth inning after coming in for Dan Haren, getting a 3-2-3 double play with the bases loaded and then, following an intentional walk, striking out Cards pitcher Shelby Miller to end the inning.