The duo dazzled the judges in the free skating to finish first after struggling in the short programme.
They had been third after the first stage of the competition but jumped up the rankings with 140.53 points in the free skating, giving them the winning score of 205.77 points.
James said: "We’re both happy with the fight today, especially after a disappointing short program yesterday. We're very proud to have our second gold medal at a Grand Prix."
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American pair Tarah Kayne and Danny O'Shea took the silver medal, scoring 191.43 points with their fourth place in the short programme and second in the free skating.
Overnight leaders Aleksandra Boikova and Dmitrii Sozlovskii dropped down to the bronze medal position.
The Russian duo finished with 189.84 points, just 1.89 points clear of fourth-placed pair Tae Ok Ryom and Ju Sik Kim, of South Korea.
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