The right-hander, who said he had trouble sleeping Saturday night, allowed four hits and walked two. His 28-pitch outing included only fastballs and changeups.
Carlos Gonzalez had an RBI single and Michael McKenry a two-run double against Garza. He signed a four-year, $50 million free-agent deal in the offseason after playing for the Cubs and Rangers last year.
Colorado starter Jorge De La Rosa also had command trouble.
De La Rosa gave up a leadoff home run to Rickie Weeks and was lifted with two outs in the second after allowing four runs. He gave up four hits with two walks, a wild pitch and a throwing error.
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