The Russian's win was an exhibition in sharp shooting that propelled her ahead of her rivals.
Pyleva missed only one target which meant that she was handicapped by only one penalty loop in her winning time of 31 minutes 7.7 seconds.
Germany's Kati Wilhelm finished 5.3 seconds back to take silver, with Irina Nikoultchina of Bulgaria in third.
Wilhelm had started with a 16 second lead after winning the 7.5K sprint, but any advantage soon evaporated when she missed three targets in her first shoot.
In stark contrast, Pyleva, a former nordic skier, performed to near perfection.
The 26-year-old had started the day in eighth position, one minute and three seconds behind Wilhelm.
But despite her accuracy, the Siberian's win was only confirmed at the last shooting stop when Sweden's Magdalena Forsberg choked with victory in her sights.
"When I saw Magdalena and Kati leaving the last shooting I thought they had made only one mistake each," Pyleva said.
"I just kept on skiing as hard as I could and when I saw both of them still doing their penalty loops, I realised what position I was in.
"Is it fair? In the biathlon nothing is fair. I'm just lucky everything came together." she added.
Forsberg, who despite dominating the sport in the past five years has yet to add Olympic gold to her collection, eventually finished sixth after being condemned to completing three penalty loops.
"I was struggling today and had to fight all the way through the race," Forsberg, a five-time consecutive World Cup winner, said.
"I have two bronze medals from these Olympics, but I'm not going to deny it would have been nice to have a gold medal before I finish my career."
Liv Grete Poiree of Norway also paid a heavy price for wayward shooting at the last stop.
Her two misses gave Nikoultchina the chance to pass her on the finishing straight and claim the bronze, 8.1 seconds behind Pyleva.