PHOENIX (AP) -Arizona pitcher Randy Johnson was put on the 15-day disabled list for the third time this season, sidelined Tuesday because of a sore back right before his scheduled start at St. Louis.
The Diamondbacks promoted 22-year-old righty Yusmeiro Petit from Triple-A Tucson to pitch in Johnson's place.
Johnson is 4-3 with a 3.81 ERA this year. The 43-year-old lefty had back surgery last October and recently was diagnosed with a herniated disk.
Johnson began the season on the disabled list, then returned to the DL on June 11. The latest move was made retroactive to June 29.
Petit pitched once for Arizona earlier this season. He lost 2-1 at San Francisco on April 22, giving up two runs and four hits in seven innings.

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