The United States defeated the Czech Republic on Monday, while defending champion Sweden was upset on the third day of the women's world curling championship.
Debbie McCormick's rink, which lost to Canada and Sweden on Monday, took a 6-4 lead into the 10th end where the Czech Republic had a chance to win with the last-rock advantage.
Czech skip Hana Synackova could have scored three points with a double takeout, but left a U.S. stone in the house, allowing the Americans to steal another point for a 7-4 win.
"It was scary at times," McCormick said. "I felt like we played well. I missed a couple of my last shots and they called a good game."
The United States, which won the tournament in 2003 under McCormick, improved to 3-2 in the round-robin draw while the Czechs dropped to 1-4.
"We're getting better, but we haven't found our `A' game yet," McCormick said.
In the day's biggest upset, two-time defending champion Sweden was defeated by Switzerland, a team that entered Monday's games with just one win.
In the 10th end, Switzerland skip Silvana Tirinzoni made an open hit for four to win after Sweden skip Anette Norberg wrecked on a guard.
The four in the 10th gave Switzerland a surprise 8-6 win over the Olympic champions. Switzerland improved to 2-3, while Sweden dropped to 3-2.
Canada, which improved to a perfect 5-0, scored three in the fifth on its way to a 9-0 thrashing of winless Italy which conceded after Kelly Scott's rink scored two in the sixth end.
"It was harder than it looked," said Scott. "A lot of points were scored on the last rock. We're pretty precise on our shotmaking right now and that's making things easier for us."
Canada will have a chance to improve to 6-0 when it takes on host Japan later Monday.
Earlier, Japan, led by Skip Moe Meguro, scored two in the sixth on its way to a 6-5 win over Italy and improved to 3-2. Scotland defeated China 6-5 to pick up its fourth win against one loss, while China fell to 3-2, reports AP.
The world championship, the first to be held in Asia, runs from March 17-25 and features 12 countries.