Karstens exited the start after feeling tightness in his right groin. Karstens threw one practice pitch, felt pain and walked off the mound. He will be treated tonight reevaluated tomorrow.
Prior to being pulled, Karstens threw 63 pitches over 4.1 innings. He allowed two runs on three hits with no walks and five strikeouts. Both runs came after Karstens was removed from the game. He gave up a double and a single before getting injured. Right-hander Duke Welker replaced Karstens and gave up back-to-back singles to score both earned runs.
Karstens was expected to come off the disabled list and make the start for Pittsburgh next week in Baltimore for Interleague play. He was placed on the DL on April 18 with right-shoulder inflammation.