The two-time world championship bronze medallists earned their best-ever component mark — for presentation — and will take a season's best overall score of 74.70 points into the long program. Duhamel pumped her fist after concluding their routine choreographed to Ginette Reno's "Un peu plus haut."
"The component elements have always been considered our weaker side," said Radford. "To finish ahead of the Russian pair who are extremely strong technically is a big step for us. We were really in the moment tonight. Nothing could stop us."
Olympic silver medallists Ksenia Stolbova and Fedor Klimov of Russia go into Saturday's free program in second with 72.33, while Wenjing Sui and Cong Han of China are third, with 66.66.
Duhamel, from Lively, Ont., and Radford, from Balmertown, Ont., are enjoying a standout season, with victories in both their Grand Prix events — Skate Canada International and NHK Trophy in Japan. Still, Duhamel said she was battling nerves Thursday.
"I didn't know what to expect and I was hoping I would get into the zone. Once the music started and we were very together going into our first element I knew we were going to be alright," she said.
They opened the program with a triple twist lift followed by side-by-side triple Lutzes and a throw triple Salchow.
They added a quad throw Salchow — Radford throws Duhamel four revolutions through the air — to their long program this season. Russians Yuka Kavaguti and Alexander Smirnov are the only other skaters attempting the move this season.
Julianne Seguin of Longueuil, Que., and Charles Bilodeau of Trois-Pistoles, Que., lead after the pairs short program of the Junior Grand Prix Final. Four Russian couples follow in the standings including Lina Fedorova and Maxim Miroshkin just 0.18 behind the leaders.
"We couldn't be happier with our performance," said Bilodeau. "We executed all our elements and achieved level fours even on our twist for the first time. It gives us a lot of confidence for the free program."
Mackenzie Bent of Uxbridge, Ont., and Garrett MacKeen of Oshawa, Ont., are fourth after the junior short dance while Madeline Edwards of Port Moody, B.C., and ZhaoKai Pang of Burnaby, B.C., are fifth.