Kowalczyk and Poltoranin were victorious in the sprint classic events with the women's and men's 10km and 15km freestyles respectively next up before attentions turn to Val di Fiemme.
World Cup leader Kowalczyk responded to an early break from France's Aurore Jean after 200m to take a lead she would not relinquish, crossing home first with a comfortable 2.8-second advantage.
She built ground on the rest of the field after the first climb and, despite it looking like Marit Bjoergen was cutting it down in the second lap, Kowalczyk cruised to a time of 3:56.0minutes.
Bjoergen broke away herself on the second lap for second place with Anne Kylloenen of Finland taking third after a tight battle with Jean and Katerina Smutna 3.2 away from the Norwegian.
Meanwhile Poltoranin was an even easier winner in the men's classic sprint breaking away early to win by 5.4 ahead of home hope and World Cup leader Dario Cologna.
Cologna was made to work hard for second place by Federico Pellegrino but beat the Italian 0.6 for it while American Andrew Newell was three seconds back in fourth.