Olympic Women’s Soccer Updates: U.S. and Canada Meet in Semifinal

The most notable development of the half, then, was the loss of the American goalkeeper Alyssa Naeher, who crumpled to the grass in pain around the 20th minute after landing awkwardly on her right leg and bending it the backward. She was on the ground for about five minutes, and tried to stay in the match.

But when she attempted a goal kick a few minutes later, she immediately grimaced and waved toward the sideline. She left the game in the 30th minute, handing the baton to Adrianna Franch, her backup.

Naeher immediately rolled over in obvious pain, and the game was stopped so she could receive treatment. Lying on her back and then sitting up, she was attended to by two U.S. trainers for about six minutes before deciding to stay in the game.

But about four minutes later, after the United States won a goal kick, Naeher took it and, swinging her right leg hard for the first time, aggravated the injury. She hopped on her landing, realized she could not continue and waved to the bench immediately, calling for a substitute.

Adrianna Franch, who had quickly warmed up while Naeher was being treated initially, sprinted on to take her place.

Naeher left the field by the closest route possible — the end line behind her goal — and then slowly limped her way around the corner flag and back to the United States bench.

By the time she was close enough for her teammates to come out to greet her, Naeher appeared to be wiping away tears with her yellow jersey.

Naeher had been the only U.S. player to play every minute of the Olympic tournament entering Monday, but it was her heroics on Friday, when she made several diving saves and blocked a late penalty kick against the Netherlands, that showed her real value.

She made two more saves in the penalty shootout after the U.S. and the Netherlands played to a 2-2 tie. Her final stop booked the Americans’ ticket to the semifinals.

The United States had a rougher go in what was, in hindsight, a tougher group: It lost to Sweden (3-0), thumped New Zealand (6-1) and then played a dreary scoreless tie against Australia to finish second in the group. That set up Friday’s World Cup final rematch against the Netherlands, which the Americans won on penalties with an immense debt to goalkeeper Alyssa Naeher.

Canada has scored only four goals in four games. The United States has eight, which is one fewer than it has had called back for offside.

But there’s more. Becky Sauerbrunn, Crystal Dunn, Lindsey Horan and Adrianna Franch, all of the United States, are teammates on the Portland Thorns with Canada’s captain, Christine Sinclair. Canada’s Kailen Sheridan plays with Carli Lloyd in New Jersey, and Erin McLeod is teammates with Alex Morgan in Orlando. Kadeisha Buchanan is a star at Olympique Lyonnais Féminin. But so is Catarina Macario.

On and on it goes.

There are so many connections between the players on the American and Canadian teams, in fact, that it would take a while to find a single player from one side who hasn’t played — at a college, at a club, in a city — with someone on the other side today.

Even their clubs teams are torn.

That means there will be a lot of friendships on the field today, but also a lot of inside knowledge. Tendencies and favorite moves, but also triggers, too.

International soccer routinely puts such relationships under tension, and never more so than today. So expect some handshakes before and after, and some hard tackles in between.

No one wants to go home to the N.W.S.L. and hear about a loss for the rest of the year.

On their face, the changes feel like part of the rotation that the team has employed throughout the tournament. But the insertion of Lavelle, a far more attacking player, for Mewis, and restoring Morgan in a partnership with Tobin Heath and Lynn Williams, suggests a forward-looking approach is coming.

Davidson has been excellent in her appearances, too, and hardly a step down from Dahlkemper, who has had a handful of dodgy moments.

This feels like a team looking to score goals and play on the front foot. That’s what the players prefer, and what the fans prefer. Today, it appears, it is also what Coach Vlatko Andonovski prefers.

The game in question is the teams’ meeting in the 2012 Olympic semifinals in London, a rollicking 4-3 American victory that, from a United States perspective, stands even today as a signature moment of grit and perseverance. Canadians describe that game — a match they led three separate times — with a different vocabulary. “Robbed” is the most common term. Others are unprintable here.

“We feel like it was taken from us,” the Canadian captain Christine Sinclair said after the game. “We feel cheated.”

Sinclair, Canada’s greatest player, will have felt more aggrieved than most. She scored three times that day in Manchester, England, only to watch the Americans respond each time and then walk off with a last-minute winner by Alex Morgan.

The Canadians have been seething ever since, driven by some dubious refereeing that had led to the tying goal, and a persistent second-class status in the rivalry that, from a Canadian perspective, should have ended that day.

The Americans went on to win the gold in London, and Canada won the bronze, a feat it repeated in Rio. Now it has a chance, again, to rewrite that day in 2012. It has already closed the gap: More than half of the meetings since 2011 have been ties or one-goal American wins.

“In 2012, we were kind of on a hope and on a prayer,” Canada’s Desiree Scott said Sunday. “We were hoping we could get to that match, but now we truly believe in ourselves and what we can do on a soccer pitch, and we believe we can get to that gold medal game.”

The United States will not need to be reminded about that day in 2012. Five Americans — Morgan, Carli Lloyd, Kelley O’Hara, Tobin Heath an Megan Rapinoe — played in it, and every member of the squad knows the danger that Sinclair, a fixture of the National Women’s Soccer League, brings to every match.

“This is probably going to be our hardest game: We know that, and we are preparing for it that way,” U.S. coach Vlatko Andonovski said Sunday. “It’s a semifinal — it’s four of the best teams in the world.”

The United States made a point of rewarding its alternates during the group stage. Catarina Macario, Jane Campbell and Casey Krueger cleared the bar when they were in the 18-player team against New Zealand, and Lynn Williams did the same against Australia. (Williams, with a goal and an assist against the Netherlands in the quarterfinals, has since proved even more valuable.)

Sweden, Canada and Brazil (which was eliminated in the quarters) also have made sure to use all their players. Now they just need to make sure they have a medal to collect.