He had made the opening goal for Malcolm Christie, before adding a second himself after the break.
In the first half, he had been denied by keeper Navarette - but he could do nothing to stop the 18-year-old opening his account with a low drive for Howard Wilkinson's side with 15 minutes to go.
Before the game, Wilko had described him as "among the cream of English football in his age group."
And Tony says: "I'm delighted he got the opportunity to get his first cap for the under-21s and obviously for a striker to score on his debut was very pleasing.
"Even the first goal was going in but got a deflection from the goalkeeper to push it into his colleague's path.
"But he can be certainly pleased with his overall performance as well as the goal.
"I think I was a little surprised that he was in the squad because he had no inkling of that having been in the under-18s all season.
"But the under-21s were depleted because of injuries and senior call-ups, so there is always a chance for the young pretenders to get an opportunity.
"With Jermain playing league football and getting so many goals this season, one could say this was a natural progression for him.
"I know he was delighted to get the call, and delighted to score; it was a good game to go in because they dominated in terms of possession.
"What it's done more than anything is show Howard Wilkinson and the coaching staff that he is capable of stepping up to that grade - maybe he will become part of that squad on a more regular basis from here on in.
"And I'm sure whoever becomes the first team manager will make him part of the first team squad.
"Then it's up to him to impress; he got a run at Middlesbrough, and, although fairy stories don't happen every game, it was a good experience for him."
Steve Bywater came on at half time and comfortably kept a clean sheet in a 3-0 win.