Players held a banner which simply read 'qualified' in front of their fans, despite needing one more victory to seal a place at Qatar 2022.
Gregg Berhalter's men must avoid losing by six goals against Costa Rica in their final qualifier on Wednesday to book their place in the tournament in eight months time.
Should the USA suffer a defeat of six goals or more, they would have to settle for a World Cup play-off place.
Chelsea forward Christian Pulisic claimed the banner was a mistake, and not the fact the players are getting ahead of themselves.
"The guys didn't know at all what it said. It was just handed to them," he explained.
"Once we realised - there's no need to show that off because we still have a job to do.
"We honestly approach it like any other game. We're going to prepare exactly the same as we would if we needed a win."
USA boss Berhalter also reiterated his star's comments after the match.
"We made a big step towards our goal of qualifying for the World Cup," the coach said.
"We know we're not there yet despite what that banner might have said.
"We still have a game to go and it's a difficult game in Costa Rica so our job right now is to recover, do regeneration and then get healthy guys, fit guys, on the field and go compete in San Jose, where we've never won before."
USA defeated Panama 4-0 in October 2017, and needed a draw against Trinidad and Tobago four days later to secure a place in the World Cup in Russia.
However, they suffered a shock 2-1 defeat which ultimately resulted in them missing out on the tournament altogether.
The victory on Sunday also saw Pulisic net his first international hat-trick.
He scored twice from the penalty spot, while finishing it off with a stunning strike.
His unusual celebration caught the eye, however, as the 23-year-old dropped down to do 'the worm', but it didn't last long as he was quickly congratulated by his teammates.
Pulisic explained the celebration was done to honour a fan, Mason Ogle, who the players met before the match.
Ogle has been diagnosed with osteosarcoma, a type of bone cancer, and was recognised as the matchday ambassador.
Despite chemotherapy and a prosthetic knee, the 15-year-old has continued to play with his high school soccer team.
Ogle met with the team when they trained ahead of the clash and made the celebration request to Pulisic.
"I met someone really special yesterday," Pulisic said at full-time.
"His name was Mason, and his one request was that if I scored, he wanted to see a worm celebration. That's what that was for."
Teammate Jesus Ferreira insisted he has no idea Pulisic would pull off the move.
"I had no idea that was gonna happen," Ferreira said.
"When it happened, I was surprised but excited. I think, when you score goals, the best thing is the celebration, and he did the worm celebration, so I'll rate it like a solid eight. Can't give him a 10 because he didn't go back down."
Meanwhile, winger Paul Arriola added: "I probably give him a five just for flexibility. I felt like he could have been a little more flexible in his worm, but I mean, I can't do that. So who am I to judge?"