Chapman, a candidate to close games this year, had not allowed a run in his first four Spring Training appearances.
Downs, who is a reliever, got the start for the Astros after the club decided to throw Brett Oberholtzer in a Minor League game earlier in the day to avoid pending rain showers. The Astros followed Downs with a steady diet of relievers.
Left-hander Alex Wood started for the Braves and threw five scoreless innings, allowing two hits. He's yet to allow an earned run in four starts.
Up next: Left-hander Dallas Keuchel, who hasn't allowed a run in three spring outings covering nine innings, will try to fortify his spot in the rotation when he starts against the Marlins in Jupiter at 12:05 p.m. CT on Tuesday (listen on Gameday Audio). Keuchel is scheduled to throw about five innings.
Brian McTaggart is a reporter for MLB.com and writes an MLBlog, Tag's Lines. Follow @brianmctaggart on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.