Poltoranin has scarcely been near the top ten during this season's Tour de Ski, let alone the top three, finishing a best of 13th overall in the sprint on New Year's Day.
However the Kazakhstani cross-country skier finally came to the fore in the fifth stage, a 5km classic individual in Italy, comfortably winning a time of 12:37.9 minutes.
Poltoranin's win doesn't drastically shake up the overall Tour de Ski standings though with Northug still leading after trailing the 25-year-old by eight seconds for second.
Champion for the past two Tours, Dario Cologna, was just 0.2 further adrift in third to jump up to second overall and prevent Northug from extending his lead too much
Alexander Legkov, second at the start of the day 5.7 seconds behind Northug, had to make do with fifth 15.7 behind in total with his Russian teammate Dmitriy Japarov fourth.
Northug heads into the penultimate stage, a 15km classic mass start, in Val di Fiemme now leading Cologna, who was 10.9seconds behind prior to the start, by 16.1.
Legkov drops to third 23.4seconds shy in total with Russian teammate Maxim Vylegzhanin, who was tenth in the 5km classic individual, fourth 42 behind Northug.