The 26-year-old said his shoulder felt strong, and he was happy with the location of his offspeed pitches.
"My arm is not in pain, and everything feels fine," said Chacin, who was 14-10 with a 3.47 ERA for the Rockies in 2013. "My ball was moving very well and I was controlling the ball all game. There were just a couple here [or there] that were off a little bit, and I threw just one bad pitch."
Chacin spent most of his start focusing on locating his array of pitches.
"I really don't worry about my velocity," said Chacin, who made a career-high-tying 31 starts for the Rockies last season. "If my ball is moving, my breaking ball is good and my arm feels good, that's more what I'm worrying about."
Chacin said his shoulder strain likely occurred because he was not delivering the ball "the right way" or with the correct arm angle while ramping up his offseason throwing regimen heading into the season. He could rejoin the Rockies as early as next week, and he said he would be ready if called upon even though he has pitched just 12 innings in his three rehab starts this month.
"I feel good, but I haven't thrown that many innings, so I don't know," said Chacin, the Rockies' Opening Day starter a year ago. "I haven't pitched five [full] innings yet, so I don't know what they're going to decide. My arm is feeling good, and I just need to get my innings and throw more pitches."
Chacin needed just 22 pitches to retire the first six batters he faced, but ran into trouble in the third. After giving up a hit to Logan Watkins, Chacin walked Eli Whiteside after a nine-pitch at-bat and gave up his first run when Chris Coghlan doubled Watkins home from second.
He followed a 26-pitch third inning by throwing 21 in the fourth, when he surrendered two unearned runs after giving up a double to Whiteside. Chacin got the first two outs of the fifth before being lifted for Pedro Hernandez with a runner on second base and the Sky Sox trailing, 3-0.
Iowa's Chris Valaika doubled home a run off Hernandez for a 4-0 advantage, accounting for Chacin's other earned run. The Sky Sox lost the game, 9-0.
Regardless of the outcome, Chacin said he felt he made progress at Security Service Field.
"I'm just trying to get stronger every time, and I feel I'm getting there," he said.
Chacin entered Thursday's game 0-2 with an 8.59 ERA in two rehab starts for the Class A Advanced Modesto Nuts.