The result meant the Gold Cup champions will play Group C runner-up Curacao in Sunday's quarter-final in Philadelphia.
The tiny Caribbean island qualified for the Gold Cup for the first time in 2017 but had never scored a goal until this year's edition.
"Curaçao is a team we can't take lightly, we know that for sure," United States coach Gregg Berhalter said on Twitter. "To me it's a Cinderella story... it's what the @GoldCup is about."
Panama, who finished second in the group with six points, will take on Group C winners Jamaica the same night.
The United States completed the first stage with three clean sheets and scored 11 goals without conceding any in a group that also included Guyana and Trinidad and Tobago.
Berhalter started the match with a completely different team from their previous two games, meaning the side have used 22 of their 23-man squad in the three matches.
"The decision to start 11 new players was an easy one," the coach said. "We believe in the group... we wanted to show that."
(Reporting by Andrew Downie; editing by Sudipto Ganguly)
