Neither side could score after the fifth inning until they combined to tally eight times in the 14th.
Colorado won its third straight over the Giants and expanded its lead over San Francisco to four games in the National League wild-card chase.
San Francisco appeared to have wrapped up the win in the top of the 14th with a three-run inning, keyed by triples from Edgar Renteria and Eugenio Velez.
Brandon Medders then came on for his third inning of work in hopes of nailing down a San Francisco victory.
Medders walked Dexter Fowler to open the inning and, one out later, Justin Miller (2-3) relieved Medders.
Chris Iannetta singled Fowler to second and Troy Tulowitzki walked to load the bases. Pitcher Adam Eaton was left in to bat and he also walked to force in a run. That brought up Spilborghs, who hit his seventh homer of the season.
Eaton (3-5) got the win despite giving up all three runs in the top of the 14th.