On the eve of the World Cup, many Americans seemed indifferent or outright pessimistic about the tournament.

Ticket prices were sky high. There were worries about immigration enforcement around the games. The courting of President Trump by FIFA, world soccer’s governing body, soured the mood for many critics of the president. And, some wondered, how would foreign visitors react to a host nation whose image was in the tank in almost two-thirds of countries polled by Pew this spring?

Weeks later, there’s a totally different feeling.

The U.S. team rattled off two impressive wins to advance to the knockout rounds, and will play Wednesday night in Santa Clara, Calif., against Bosnia and Herzegovina.

And those foreign visitors? Well, they have had a great time, joyously posting on social media about their encounters with Americana during their sightseeing adventures: Buc-ee’s, the quintessential road trip pit stop; hotel ice machines; unlimited chips and salsa; ranch dressing. The videos became so popular that fake ones also circulated, but there was genuine tourist astonishment at offerings Americans have taken for granted.

“The enormous portion sizes!” said Philip Labas, a resident of McHenry, Ill., mimicking how foreigners have expressed amazement at some of America’s culinary customs. “Free refills! Unlimited chips and salsa! It’s the American way.”

Mr. Labas, who drove on Route 66 from Chicago to Southern California to see the U.S. team play and encountered many fans from abroad along the way, continued, “I believe there is a positive vibe around the World Cup, there’s a positive vibe around this men’s team and I think people are leaning in to it.”

At a moment when national pride is at a quarter-century low, according to Gallup, Americans, even for a fleeting moment, have found something to unite around.

Douglas Hartmann, a sociologist at the University of Minnesota, said that the ways foreign visitors have celebrated and been amused by the small things have brightened the mood of Americans who may be down on their country.

He said that many Americans, particularly liberals, have been reluctant to be outwardly patriotic, even if they still love their country. But seeing international visitors appreciate the United States, along with watching their team advance, has given them reasons to cheer the nation.

“I think it’s given a lot of Americans, especially on the liberal side, almost permission to be patriotic,” said Mr. Hartmann, whose specialties include American society and sport studies.

Meanwhile, he said his conservative friends and family, who aren’t soccer fans, have embraced the men’s team’s success so far. “They hate soccer,” he said, “but they love America’s dominance. Finally, we’re showing everybody.”

“It’s a rare meeting point that is bringing Americans together across the usual polarized dividing lines right now,” he added.

Wednesday night’s game in the Bay Area comes just ahead of the Fourth of July weekend and the nation’s 250th birthday, adding a patriotic luster to an event many Americans were glumly approaching, given those divisions.

Justin Hobbs, 50, who attended a game last week between the United States and Turkey outside Los Angeles, said that he was glad to see the World Cup uniting Americans.

“You look at all the fans here from all over the world,” he said. “They are making themselves part of the cities. It’s exciting to see. And it’s bringing us together as a country.”

Mr. Hobbs, who is from Tulsa, Okla., said the World Cup has him feeling better about the country ahead of the holiday weekend. He was dressed in red, white and blue, from his headband down to his socks and sneakers.

“I wanted to wear this,” he said, “because I felt this was embodying who we are as Americans, especially with the 250th coming up.”