Sullivan made a brilliant near-post run in the box, being lined up as their attacking midfielder in a 4-3-1-2 formation, slotting past the goalkeeper in tidy fashion.
He now awaits his MLS debut, with first-team boss Jim Curtin watching as he awaits to call him up to the squad.
One of the highest-rated youth products in U.S. Soccer's storied history, the 14-year-old will move to Manchester City upon turning 18 in 2027 and City will pay up to $5 million (£4m/€4.6m).