The Italian won the race in a time of 39 minutes and 54.4 seconds, to claim the first gold medal of the Games.
Larissa Lazutina of Russia grabbed silver, a further 1.8 seconds behind and Katerina Neumannova of the Czech Republic took the the bronze.
Belmondo, who is a veteran at 33, had to called upon all her resolve to take the lead from Lazutina in the final 30 metres in what was a thrilling finish.
"I broke my pole at the 10.5 km mark and lost around five or six
Olympic champion Stefania Belmondo
Belmondo has now added a second gold to her Olympic collection, that also includes two silvers and four bronze.
Earlier in the race, Russia's Julia Tchepalova, who eventually finished fourth, grabbed the lead, before she was caught by 15 other skiers, including Belmondo - who had broke her pole with 4.5km to go.
By the 13.7km mark, Tchepalova's compatriot Lazutina took the initiative to head the pack, along with what was now just a group of six.
And when Lazutina broke clear, it was the Italian who took up the challenge - a decision that proved to be very fruitful.
"Today I'm very, very happy. It's simply incredible," said Belmondo.
"I broke my pole at the 10.5 km mark and lost around five or six seconds. A French guy ran up and handed me a pole, but it was too short.
"Eventually my coach got a pole to me and when I caught up with the group I knew I could catch up," added Belmondo.