The midfielder came off the bench and finished sharply from just outside the box, intercepting a poor clearance from the Dundee goalkeeper to make it 3-0 before Dwight McNeil added a fourth late on. Foster's involvement came as something of a surprise even to himself, having found out only the night before, after playing for Everton's Under-21s in a 2-1 defeat to Oldham Athletic on Friday, that he would be involved with the first team the following day.
"It was good. It was a stadium full of fans and with the first team - it is the stuff of dreams. And then to score is just an add-on. I wasn't sure if I was going to be with them at the start of the week, I'm very grateful," Foster said, reflecting on the milestone afternoon.
On the goal itself, he added: "I'm just happy to contribute... As long as it contributes to the team winning, that's the main thing."
Foster was among a group of academy players given opportunities during Everton's training camp in Scotland, alongside Malik Olayiwola, Braiden Graham, George Finney, Will Tamen, Eli Campbell and Joel Catesby. The midfielder praised David Moyes for the guidance he and his fellow academy graduates had received since stepping up.
"He's been great. Honestly, the set up with me and the lads, I know we have only been with him a short time but every one of the U21s that have been up, he's spoken to us, talked to us about our game and it has been really good."
Everton's dominant win over Dundee, in which Beto and Thierno Barry also found the net, gave Moyes an early look at his squad depth before the campaign proper begins, with several senior players, including Jarrad Branthwaite, James Garner and Vitalii Mykolenko, still absent from the matchday squad.
At Under-21 level, Foster has established himself as a graceful, composed presence in the deeper midfield areas, and he carried that assurance into his senior bow, looking calm on the ball throughout his time on the pitch despite the step up in intensity.
His ability to remain unfazed in front of a full away following will have caught the eye of Moyes, who fielded a raft of youngsters across both halves as Everton wrapped up the opening fixture of their pre-season schedule.
With the World Cup having taken a significant chunk out of Everton's available options for the trip to Scotland, Foster's emergence offers Moyes a timely reminder of the depth building behind his first-choice group.
Whether he features again before the visit of Bolton Wanderers, Everton's next fixture, may hinge on how the head coach chooses to manage his squad as more senior players return from their summer breaks in the coming weeks.