Chacin has been the Rockies' best pitcher this season, going 3-0 with a 1.46 ERA in four starts. Opponents are hitting .193 against the right-hander, including an average of .128 (6-for-47) by right-handed hitters and .278 (10-for-36) by lefties. Chacin has six walks and 16 strikeouts in 24 2/3 innings.
"His changeup and his slider were real good," manager Walt Weiss said. "And he had fastball command, which is big for Jhoulys. His changeup is a plus, plus pitch, the fact that he can throw it to right-handers, he can throw it to left-handers regardless of the count, to get him back in counts, to finish hitters. I think that's been one of the keys for him.
"His arm speed on his changeup has been really good. The other secondary pitch he's got is his slider, which has been really good. He's had it all working early on."
Weiss said a corresponding roster move will be announced after Saturday night's game or on Sunday morning.
Tyler Chatwood started twice in place of Chacin and could be kept if the Rockies decide that Juan Nicasio would benefit from time at Triple-A Colorado Springs. Nicasio has thrown five or fewer innings in five straight starts, and in four of them, he has thrown between 92 and 95 pitches. Nicasio's next turn in the rotation would be Wednesday against the Yankees.