Undefeated Brad Jacobs and his Northern Ontario rink didn't like how their game against Team Canada's Pat Simmons began as Simmons counted three in the first end, but they bounced back for a 10-6 victory that left them a perfect 4-0.
After seven draws, Jacobs was the lone unbeaten team. Alberta's Kevin Koe beat brother Jamie Koe 8-7 in the afternoon and then topped Manitoba's Mike McEwen 9-4 to collect his fourth win.
The Alberta skip was alone in second place at 4-1 while Brad Gushue's Newfoundland and Labrador rink was in third at 3-1.
Ontario's Glenn Howard defeated New Brunswick's Mike Kennedy 9-6 to move into a tie at 3-2 with Simmons, who dropped a surprise 6-4 decision to Prince Edward Island's Adam Casey earlier in the day.
"In this Brier, if you give an inch, and we gave a few out there, they're going to bite you," said Canada third John Morris. "It doesn't matter what team you're playing."
McEwen and B.C.'s Jim Cotter were at 2-2 while Laycock moved to 2-3 after topping Quebec's Jean-Michel Menard 7-3 in the evening.
Round-robin play continues through Friday morning.
"I think we're one of the favourites, one of a group of four, five, six or seven teams," Gushue said. "It's nice to be in that but I don't think we're coming in here with people gunning for us.
"I think they're gunning for everybody."
Simmons suffers 1st loss
Team Canada has its first loss on Monday afternoon.
Simmons dropped a 6-4 decision to Adam Casey of Prince Edward Island, leaving Northern Ontario's Brad Jacobs (4-0) as the lone unbeaten team in round-robin play.
Brad Gushue of Newfoundland and Labrador defeated Saskatchewan's Steve Laycock 7-5 and Alberta's Kevin Koe edged Jamie Koe of the Northwest Territories 8-7 in an extra end.
B.C.'s Jim Cotter defeated Ontario's Glenn Howard 9-5 in the other afternoon game.