Canada's Chelsea Carey suffered her first loss at women's curling world championship on Monday, falling 6-3 to Russia's Anna Sidorova in Draw 6.
Russia (3-1) played conservatively in the early going, capitalizing on a missed takeout by Canada (3-1) in the seventh end for a decisive two points.
Carey's Calgary-based rink was the last undefeated team at the tournament as Japan (3-1) was upset by Denmark (2-2) earlier in the same draw.
Canada faced Sweden's Margaretha Sigfridsson in the evening draw.
Sidorova is a two-time European champion and has won bronze twice at the world championships.
This is Carey's first world championship, and Canada hasn't won gold at the event since 2008.
Russia opened with a hit and roll for a deuce in the first end, followed by a scoreless second.
Carey took a 3-2 lead in the third end with a smooth tapout for the triple.
Sidorova continued her conservative play in the fourth, going for the blank and keeping the score 3-2 in Canada's favour. She did the same in the fifth and sixth ends to keep the hammer.
Carey missed a takeout in the seventh end, instead tapping the Russian rock closer to the button. Sidorova, with the hammer, threw an easy draw for two and a 4-3 lead.
Canada was too light on its attempt at a tap in the eighth end, giving Russia another point.
The struggles continued for Carey in the ninth end as she failed on an attempted triple takeout. Instead, Russia stole a point to make it 6-3 heading to the final end.
Sidorova kept the house clear in the 10th end, with the Canadians shaking hands with a stone still to throw.