The Philadelphia Union teenager, who is set to join Manchester City, scored at just 17 years and five days old to break the record that had been set only days earlier by fellow teenager Mathis Albert.
Sullivan produces a moment of history
Sullivan doubled the United States’ advantage in the 62nd minute with a superb finish.
The 17-year-old applied pressure to Mexico goalkeeper José Rangel, intercepted a misplaced pass and calmly lifted the ball over the goalkeeper from distance and into the net.
The goal sparked celebrations from Sullivan's teammates and the U.S. bench as he etched his name into the national team's record books.
Sullivan's record came just four days after Borussia Dortmund youngster Mathis Albert had become the youngest US international goalscorer with his goal against Chile.
Albert's record therefore lasted only a matter of days before Sullivan lowered the mark again.
USA cruise past Mexico
The United States took the lead in the 28th minute through 18-year-old Julian Hall.
Hall reacted quickest after Gio Reyna's effort was parried by Rangel, scoring his third goal in as many international appearances.
Sullivan then made it 2-0 before Malik Tillman completed the scoring in the 84th minute with a fine finish into the top corner.
Mexico were reduced to 10 men in the 67th minute when Mateo Chávez was sent off following an incident involving Yunus Musah and Sebastian Berhalter.
Manchester City move adds to Sullivan's growing profile
Sullivan currently plays for Philadelphia Union but has agreed to join Manchester City next year.
His emergence has accelerated during the 2026 season, with the teenager establishing himself as one of the most exciting young players in Major League Soccer before making his senior international debut.
He has now scored in his first three appearances for the United States, while his latest goal has made him the youngest scorer in USMNT history.
Sullivan's performance also earned praise from head coach Mauricio Pochettino, who described the youngster as a fighter and a warrior while highlighting his quality.
USA maintain impressive run
The victory was the United States' third consecutive multi-goal win under Pochettino, following victories over Peru and Chile during the international window.
The Americans will now face Canada in St Paul, Minnesota, on Tuesday, while Mexico will take on Chile in Los Angeles.
USA 3-0 Mexico
• USA: Julian Hall 28', Cavan Sullivan 62', Malik Tillman 84'
• Mexico: No goals
Sullivan's historic strike marks another significant milestone in the rapid rise of a player who will soon begin the next chapter of his career with Manchester City.