Kowalczyk, competing in North America while World Cup leader Marit Bjoergen concentrates on the Tour de Ski back home, was unstoppable in the third race of three in Canada.
The 29-year-old Olympic champion powered around the course to win in 42:51.5minutes and add to her win in the 10km classic mass start at the start of proceedings on Thursday.
And, while Kowalczyk ran away with the victory, the battle for second went right down to the wire with Finland’s Anne Kylloenen winning a photo finish on the line.
As many as six were in contention coming into the final straight and it was the outstretched left ski of Kylloenen that beat Vibeke Skofterud into the runners-up spot.
Kylloenen finished 34.9seconds behind Kowalczyk while Norwegian Skofterud was 0.01 adrift in third with her teammate Kristin Stoermer Steira taking fourth another 0.08 behind.
Such was the tight nature of the finish Masako Ishida of Japan was only another 0.01 behind while Valentina Shevchenko was 0.03 away for sixth and Alija Iksanova 0.05 for seventh.