China’s Yang Qian set a new Olympic record as she won the women’s 10-metre air rifle final.
Galashina looked set to claim gold but a poor final shot allowed her China opponent to overtake her in the final seconds, despite a below-par effort of her own.
With 10.9 the highest total available on a single shot, Yang won with an overall score of 251.8, ahead of Galashina on 251.1.
Switzerland’s Christen was further back on 230.6.
Team GB’s Seonaid McIntosh was knocked out in qualification.
Later on day one, the men’s 10m air pistol gold medal will be up for grabs, along with medals in eight other disciplines.
The biggest event on the first day is the men’s road race, which features four Team GB representatives in Geraint Thomas, Tao Geoghegan Hart, Adam Yates and Simon Yates.