The 23-year-old profited from being first on track after a fresh sweep of thick snow in Germany, making conditions ideal for her to lead with a 53.932s run.
Snowfall worsened and officials cancelled the second run, awarding gold to a racer whose highest-ever overall World Cup finish was 16th in 2016.
Home favourite Natalie Geisenberger, crowned double world champion last week, settled for silver just 0.090s back with Russia's Viktoriia Demchenko finishing third.
Geisenberger's lead at the top of the overall World Cup standings remains commanding, while Robatscher climbed to tenth.
Sir Bradley Wiggins & Lizzie Deignan