Chacin pitched 4 2/3 innings and allowed three runs on five hits. All his runs came on a three-run homer. He struck out two and walked one, throwing 61 pitches -- 40 for strikes -- while earning his second loss in as many rehab starts.
"At this point with Jhoulys, it's just a matter of getting his work in, building his arm up, and being ready to walk out on a big league field and make a start," Weiss said. "He's moving toward that quickly. He's on schedule."
Chacin was 14-10 with a 3.47 ERA for the Rockies in 2013.
Owen Perkins is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.