DENVER (AP) — Brandon Belt hit a go-ahead single and a grand slam in a 10-run first inning that propelled the San Francisco Giants over the Colorado Rockies 12-4 in a doubleheader opener. Belt connected for his home run on the sixth pitch after Jhoulys Chacín relieved, a 452-foot drive for his third career slam. Posey went deep four pitches later. Rockies starter German Márquez allowed eight runs and six hits in two-third of an inning, an outing that raised his ERA from 4.13 to 6.21. He has lost to the Giants three times this season.