Sidorova scored a deuce in the eighth end for a 5-2 lead and added two more points in the ninth for the victory at the Tsukisamu Gymnasium.
Muirhead had claimed the final playoff spot earlier in the day with a 9-4 win over China's Sijia Liu in a tiebreaker game.
Sidorova will next play the loser of Saturday's Page playoff 1-2 game between Canada's Jennifer Jones and Switzerland's Alina Patz.
Jones and Winnipeg-based teammates Kaitlyn Lawes, Dawn McEwen and Jill Officer finished the round robin in second place with a 9-2 record. Patz earned the top seed with a 10-1 mark.
The 1-2 game winner advances to Sunday's gold-medal game.
The semifinal winner will play for the gold and the loser will play Muirhead for the bronze medal.
Canada hasn't won gold at this event since Jones won in 2008 at Vernon, B.C. The five-time national champion is also the reigning Olympic champion.
Switzerland's Binia Feltscher won the 2014 world title in Saint John, N.B., defeating Ottawa's Rachel Homan in the final.
Canada leads all countries with 15 gold medals and 31 podium appearances at the world championship since 1979. Sweden is next with eight gold and 23 total medals.