Team GB romped to the first of the three straight wins they require for a top four place and a shot at a medal in the women’s tournament.
Muirhead, Vicky Wright, Jennifer Dodds and Hailey Duff came roaring back from a 7-3 loss to Canada to overwhelm Japan with two ends to spare.
“We knew that was a very important game for us and we came out with a lot of fire,” said Muirhead.
“We had a good chat after the Canada game and you couldn’t ask for better than the start we got.
"We weren't far away against Canada but I really focused hard today on not making those small errors. The team helped me make shots and we were really clinical."
Muirhead found the going tough on a personal note against Canada, shooting 69%, but raised her game at the next opportunity, shooting 78% this time.
The 31-year-old, who struggled to impose herself against Canada’s Jenny Jones, had the better of opposite number Satsuki Fujisawa from the very start.
Britain capitalised on a Japanese error in the first end, tapping out for three to make a dream start and then preventing them from replying with more than a score of one.
Muirhead took total control with another three to jump into a 6-1 lead and break the back of the contest.
The first slip came in the fourth when she clipped her own stone out of the house, allowing Fujisawa to draw in for two, but Japan couldn’t score heavily enough to turn the tide.
A score of two in the eighth saw fists bump with two ends to spare.
“To get the 6-1 lead was nice,” she said. “We didn’t get complacent and kept control of every end, every stone and saw the game out.”
Next up for Muirhead is hosts China, who were themselves beaten 10-2 by Japan, followed by Russian Olympic Committee.
“Whoever we’ve got in our last two games, they’re going to be tough,” she said. “They’re all hard games at the Olympics.
“It’s always a bit harder when you’ve got the home crowd against you as we will against China, but we’re enjoying every moment out there."We've got to take each game at a time. We wanted to get in this position and I've been in this position at the last two Olympics. We're a team that likes pressure."
Watch All the Olympic Winter Games Beijing 2022 live on discovery+, Eurosport and Eurosport app