The Philadelphia Union midfielder made his debut just moments after his brother and teammate, Quinn Sullivan, 20, scored a goal during the Subaru Park match against New England Revolution, putting their squad up 5-1.
Sullivan said he figured the historic moment would happen during either Wednesday's or Saturday's game.
"Sullivan's historic debut comes at 14 years, 293 days old when he took to the pitch in the 85th minute of the Union's match against New England Revolution," the Philadelphia Union said in a release. "Sullivan breaks the record by 13 days held by Freddy Adu who was 14 years and 306 days old."
Adu congratulated Sullivan on X following Wednesday's match.
Sullivan was the youngest player in club history to be added to the first team roster after signing an MLS record deal with the Union on May 9. He's since made five starts with Philadelphia Union II in MLS NEXT Pro and has scored in each of his last two matches.
Sullivan's contract says he'll play for Manchester City within the English Premier League when he turns 18.
Click here to follow Daily Voice Hanover-Penn Township and receive free news updates.