It was her first World Cup victory in the classic skiing event.
Diggins chalked up the win on the same course where she secured her first World Cup win 14 years ago in the Tour de Ski during the 5k skate race.
Diggins also won the women’s sprint free race on Saturday.
In 14th place, Parkite Rose Brennan was the next-best American finisher.
The annual Tour de Ski race is a seven-stage competition part of the FIS Cross-Country World Cup circuit.
The nine-day competition in Italy has four races in Toblach and three in Val di Fiemme.
Next up in the race series is the men’s and women’s 20km interval start Monday followed by a 15km classic race on Wednesday.
