Rockies 5, Giants 4: Nolan Arenado belted a two-run double with two outs in the ninth as Colorado rallied to edge visiting San Francisco in the opener of a three-game series.

Arenado’s walk-off double off Sergio Romo (3-1) scored Troy Tulowitzki and Carlos Gonzalez after the Giants pulled ahead 4-3 in the top half on Tyler Colvin’s two-out double off LaTroy Hawkins (2-0). Romo suffered his second blown save in 17 opportunities for the Giants, who have lost three of their last four.

Wilin Rosario homered and drove in three runs for Colorado, which improved to 12-3 in series openers. The Rockies got on the board in the fourth when Tulowitzki delivered a leadoff double and later scored on Rosario’s two-out double off Madison Bumgarner, who struck out six and allowed three runs over six frames.

San Francisco answered in the fifth when Gregor Blanco tripled in two runs and scored on Hunter Pence’s two-out single off Franklin Morales, who yielded three runs while striking out six over six frames. Rosario tied the game with a two-run homer off Bumgarner in the sixth, but later struck out with two runners on to end the seventh.

Brandon Hicks, Colvin and Pence had two hits apiece for San Francisco, which is 4-10 at Coors Field since the beginning of last season. The Giants played without catcher Buster Posey (back) and center fielder Angel Pagan (shoulder), but both are expected to be available Wednesday.

GAME NOTEBOOK: The Rockies activated OF Michael Cuddyer from the 15-day disabled list and optioned RHP Chris Martin to Triple-A Colorado Springs. … Giants 3B Pablo Sandoval went 0-for-4, snapping his nine-game hitting streak. The middle of San Francisco’s order – Sandoval, Michael Morse and Hector Sanchez – combined to go 0-for-12 with four strikeouts. … Bumgarner has allowed three or fewer runs in 18 straight road starts, a franchise record.