Philadelphia5 - 1New England

At the age of just 14 years and 293 days, Sullivan was brought on as an 85th-minute substitute to a rapturous applause after breaking the MLS record previously set by Freddy Adu, who was 14 years and 306 days when he first represented DC United back in 2004.

Adu has reacted on social media to Sullivan's historic home debut, posting on X: "Big congrats to Cavan Sullivan for his record breaking debut today. That's a hard record to break and the kid did it. Well done and good luck my man."

Sullivan, who has also become the youngest North American player in the top flight of a team sport, joined Philadelphia's academy at the age of 10 and made MLS history in May when he signed the largest-ever homegrown contract.

The midfielder had previously made five starts with Philadelphia Union II in MLS NEXT Pro and scored in each of his last two games before coming on for his senior debut on Wednesday, just a minute after his older brother Quinn Sullivan sealed the victory by scoring Union's fifth goal.

Record-breaker Sullivan reacts to 'chaotic' family moment

"Seeing more goals go in was great for the both of us, looking at each other like, 'this is good, this is awesome, could be a big opportunity for you to make your debut,' and it came to fruition," Quinn told Union Soccer Blog reporter Joe Tansey.

Commenting on his brother's goal and the moment he stepped onto the pitch as a senior player for the first time, Cavan said: "Absolute chaos, for sure. Awesome goal by [Quinn], great finish. Yeah, I was there to celebrate right with him.

"I think that combo of his goal and then me coming in for the sub, it was complete, like, anarchy. Honestly, one of the loudest things I've ever heard. So yeah, the stadium was electric, and it was pretty cool."

Speaking to reporters with composure beyond his years, Sullivan added: "Look, this is just the start. I'm really, really happy to have done this, but it's honestly the first box checked off, so a long journey ahead.

"I know it's all about where you finish, not where you start. So I'm just going keep working, keep developing here. My main focus is on Philadelphia and our season ahead.

"I mean, obviously, it's pretty cool to have," he later admitted when asked about breaking Adu's record. "I'd be lying if I say, I didn't want to reach for it... He really paved the way for young guys like me."

Curtin: 'Sullivan is going to get better and better'

Sullivan was labelled a "generational talent" by Philadelphia head coach Jim Curtin prior to kickoff and after the match stated that there is "a plan in place" for him to develop into a "special" first-team star.

"This is just the first chapter in Cavan's career. For those that don't know, we do have a plan for him," said Curtin. "It's not just minute by minute or day by day; there is a plan in place. So you guys saw him dominate the academy level, even up three years.

"You saw him now score some good goals for Union II and do really well. You guys don't get to see him every day in training, but the staff does, and the time was right to give him an opportunity.

"The reality is, guys, he's not a normal kid. We've known that from the start. Do I still want him to play like a kid and play with that joy in the backyard with his brothers? Of course, but he's different. And that's the reality of things.

"Because he's different, he has a different plan and a different trajectory than other players in our group, and that's the reality of the professional level. There's no such thing as too old or too young, there's only good and bad, and he's special. We can see that tonight. He's going to get better and better."

Sullivan one to watch ahead of future Man City move

Cavan is regarded as one of America's brightest prospects and has already agreed a future transfer to Premier League champions Manchester City, with the youngster expected to make the move to the Etihad Stadium when he turns 18.

"The collaboration between the Union and the [City Football Group] was - that did it for me. I always watch Man City. They're like every kid's dream team," Sullivan told ESPN at the time.

"For [Philadelphia and Man City] to come together and agree on something - I sat with my family and my agents and we decided that it was the best plan."

Sullivan could be in contention to make his first start for Philadelphia when they play host to Nashville in their next MLS fixture on Saturday.