LONDON >> The defense was stifling, even suffocating at times.

The U.S. women put on a clinic Tuesday, forcing the Canadians to take bad shots or not allowing them to shoot at all.

The Americans, who cruised into the semifinals of the Olympic basketball tournament with a 91-48 rout, harassed Canada into three shot-clock violations in the first 7 minutes.

“It’s one thing to miss a shot, but to not be able to get a shot off says a lot about your defense,” U.S. coach Geno Auriemma said. “It’s a double whammy. It brings your team closer together because it took all five guys to create that and takes the life out of the offense of the other team.”

While the four-time defending gold medalists seemingly couldn’t miss in their last game — a 114-66 rout of China — they were sloppy early on against Canada.

So they turned to their defense.

“That’s probably a better feeling than making a 3, when as a unit you found a way to stop them as a unit,” said Diana Taurasi, who led the U.S. with 15 points. “That’s really hard to do because to get a shot off isn’t the hardest thing, it might not be a quality one, but you can get a shot off.”

The Americans forced 26 turnovers and were off and running.

“We really were in sync defensively,” Candace Parker said. “Everyone knows that this team can score a lot of points, but we were locked in defensively and that will be huge going forward.”

The U.S. held Canada to the fewest points it has given up in an Olympic quarterfinals since beating Slovakia 58-43 in 2000.

“We get steals. We get deflections. We get rebounds, kick the ball out and here we go. We’re rolling.” said U.S. forward Tamika Catchings, who had four steals.

Next up for the U.S. in the semifinals on Thursday is Australia, which the U.S. has beaten in the last three gold medal games.

The Americans haven’t lost to Canada since playing in the world championship in 1975. The victory was their 39th straight in Olympic play and came 20 years to the day after the win that started the streak — an 88-74 victory over Cuba for the bronze medal in the 1992 Barcelona Games.

Canada, which was the final team to qualify for the London Games, made its first appearance in the Olympic quarterfinals. The Canadians looked timid against the Americans’ pressure defense at the start.

Taurasi said locking teams up defensively “has to be our focus.”

Despite its stellar defense, the U.S. was sloppy on offense.

The Americans missed a bunch of easy shots early on and only led 8-4 before scoring the next 11 points to take control. Parker had four points during the spurt.

Canada was able to close within 11 points in the second quarter, but the U.S. put the game away, outscoring its northern neighbors by 10 the rest of the half to lead 42-21 at the break.

Shona Thorburn’s running left-handed fling from 15 feet that banked in at the halftime buzzer was the lone highlight for Canada in the first half — when the Canadians had more turnovers (12) than field goals (six).

By the time Kobe Bryant, LeBron James and Kevin Durant showed up in the third quarter after they had finished practice, the U.S. women had doubled Canada’s score — 57-28.

It only got worse from there.

Sylvia Fowles played in her second straight game after missing three in a row to rest a sore left foot. She only played nine minutes in the win over China. She looked stronger against Canada, scoring 12 points in 9 minutes.

Kim Smith scored 13 points to lead Canada.

Despite the final outcome, Canada coach Alison McNeill was proud of her team’s Olympic run.

“We really have come far over the last few years,” she said. “It may be the last time they are together, but they should be so happy of where they have brought Canadian basketball.”

In other quarterfinal games later Tuesday, Turkey played Russia and France took on the Czech Republic.