Russia’s Sergey Ustiugov extended his lead after winning for a second successive day on stage two of the Tour de Ski in Val Müstair.
Norway's Ingvild Flugstad Østberg took the lead after winning the second stage of the corresponding women's competition in the Swiss resort.
Ustiugov, competing in the absence of many of his team-mates after they were suspended by the International Ski Federation due to being implicated in last month's McLaren Report, attacked in the closing kilometre to win the 10 kilometres mass start race.
He had won the men's freestyle sprint victory in the opening stage yesterday.
A lead group was whittled down to around 20 heading into the final lap before Ustiugov attacked to win by 1.9 seconds in 24min 50.0sec.
Martin Johnsrud Sundby of Norway finished second and his team-mate Didrik Toenseth crossed third 2.3 seconds behind.
"I had great skis," said Ustiugov.
"The service team did a great job.
"The pace was very high from the beginning.
"I did not expect I would be leaving Val Müstair with two wins and the lead in the Tour de Ski."
Ustiugov now leads defending champion Sundby by 18.9 seconds in the overall standings.
Alex Harvey of Canada lies third, 59.6 seconds behind the winner.
Østberg enjoyed a seven second victory in the women's race after crossing first in 13:21.20.
Team-mate Heidi Weng finished second seven seconds behind.
A Norwegian clean-sweep was completed by Krista Parmakoski in third, 11.4 behind.
Østberg leads Weng by 10.3 seconds in the overall category.
Sweden Stina Nilsson lies third 23.8 seconds behind the leader.
A rest day will take place tomorrow before action is due to resume on Tuesday (January 3) with a skiathlon in the German resort of Oberstdorf.
Further individual and mass start are then scheduled to be held in the Italian resorts of Toblach and Val di Fiemme on Friday and Saturday (January 6 and 7) before the Tour de Ski concludes with a climb free technique pursuit next Sunday (January 8).