Diggins, the World Cup overall leader and Tour de Ski leader, finished in 10 minutes, 51.2 seconds. Rucka-Michałek was 8.6 seconds back.
Swedish skiers rounded out the podium, with Emma Ribom second at 5.5 seconds behind and Moa Ilar third, 6.9 seconds off the lead.
The victory allowed Diggins to maintain her lead in both the overall World Cup standings and the Tour de Ski, keeping her on track for the Crystal Globe awarded to the season’s top skier.
Other Polish competitors finished further down the field.
Izabela Marcisz placed 50th, 35.7 seconds behind the winner; Monika Skinder was 56th at 41.2 seconds back; Magdalena Kobielusz finished 65th at 56.7 seconds; and Aleksandra Kołodziej was 78th, trailing by 1 minute, 34.9 seconds.
Women’s and men’s 20-kilometer classic pursuit races are scheduled for Thursday.
The Tour de Ski, one of the highlights of the cross-country skiing season, is being held entirely in Italy for the second consecutive year.
This year’s six-stage event concludes on Sunday with a 15 km mass-start race featuring a grueling climb up the Alpe Cermis peak in Val di Fiemme.
(gs)
Source: IAR, PAP