Big in Japan: Russian teen Alena Kostornaia wins figure skating Grand Prix in Sapporo
Sitting first after the short program, Kostornaia, 16, topped the free program rankings with a score of 154.96 – giving her a combined total of 240.00.
That was enough to finish comfortably ahead of 17-year-old local favorite Rika Kihira, who scored 151.95 for her free program and 231.84 overall.
Olympic champion Zagitova finished third in Sapporo with a total score of 217.99.
For Kostornaia it is a second Grand Prix title in her first senior season, after her victory at the Grand Prix in Grenoble earlier in November.
On that occasion her medal moment descended into comedy when officials mistakenly presented American rival Mariah Bell with gold, when she had in fact finished third.Also on rt.com Medal mix-up: French official gives gold to US skater instead of Russian winner (VIDEO)
With her victory in Japan Kostornaia cemented her place in the season-ending Grand Prix Finals to be held in Torino, Italy, where she will be joined by Zagitova.