The 22-year-old finished the event in Italy in a time of 26:10.9 to claim his second consecutive victory after topping the charts in the previous event in Austria in December.
This latest win was his seventh out of eight competitions this season, as he continues to look head and shoulders above the rest of the field.
Riiber's jump of 104.5m saw him lead the way after round one with a score of 146.6, with Espen Bjoernstad second on 140.8 and Franz-Josef Rehrl third with 140.7.
The 2019 World Champion's dominance continued in the 10km cross country, as he saw off second-placed Vinzenz Geiger by 26.6 seconds, while Joergen Graabak came home in third in a time of 26:38.6.
Victory in Val di Fiemme sees Riiber continue to lead the way in this year's standings on 780 points after eight events.
Graabak is the closest competitor with 511 points in second, while Geiger is some 298 points behind in third.