The 27-year-old made a positive start and took what would prove to be a crucial lead after roughly a quarter of the race was completed.
She would not surrender that advantage and sealed yet another success, following golds in the 15km individual and the 10km pursuit.
"It's amazing to be here because I dreamed about it, to be an Olympic champion, from my childhood. But to get three - dreams do come true," she said.
"I am really thankful to the people here and the atmosphere they made for me."
Domracheva's time of 35minutes 25.6seconds was just over 20 seconds quicker than her nearest rival, with Gabriela Soukalova earning silver, the Czech's first podium in these Games after two fourth-place finishes.
Norwegian Tiril Eckhoff claimed bronze after finishing 27.3secs behind, with Germany's Evi Sachenbacher-Stehle, who had been in third up until the closing stages, agonisingly missing out by exactly one second.