After six straight wins to open the tournament, Alberta lost 7-5 to Ontario's Jenn Hanna on Tuesday night. Northern Ontario chased the leaders at 5-1 with a pair of wins earlier in the day.
Defending champion Jennifer Jones downed Saskatchewan's Jolene Campbell 11-5 for a third straight win after opening 1-2. Jones and Quebec's Marie-France Larouche were both 4-2.
Campbell dropped to 4-3 alongside Saskatchewan and Nova Scotia's Jill Brothers, who was a 7-5 winner over Prince Edward Island's Suzanne Birt.
Ontario improved to 3-3 to sit tied with Manitoba's Kerri Einarson, who beat Stacie Curtis of Newfoundland and Labrador 8-5.
P.E.I. fell to 2-4, New Brunswick's Sylvie Robichaud and B.C.'s Karla Thompson were 1-5 ahead of Newfoundland at 1-6.
The top four teams at the conclusion of the preliminary round Friday advance to the Page playoff.