Kowalczyk won by nearly 20 seconds to give her a second cross-country Olympics gold. She also won the 30-kilometer, mass start race in Vancouver.
The Polish skier injured both her left foot and ankle last month and on the day after the opening ceremonies in Sochi she put a picture of the X-ray of her foot on Facebook. That picture showed a fracture, but it did not keep her away from the skiing course at these Games.
Kowalczyk covered the 10 kilometers of classic-style skiing in 28:17.8. Defending champion Charlotte Kalla of Sweden finished 18.4 seconds behind.
Kalla won her second silver medal in these Olympics, having finished second to Norway's Marit Bjoergen in the skiathlon. She has four medals in her career, including a relay gold in Vancouver four years ago.
Therese Johaug of Norway finished third, 9.9 seconds behind Kalla.
Kowalczyk received a two-year suspension from the sport in 2005 for the use of a banned substance. After further examination, it was determined she used the drug on the advice of her physician as a painkiller without either of them knowing it was on the banned list.
That suspension was eventually reduced to less than a year.