The 17-year-old Blues winger played the full the game for the young England side in their 4-0 success.
Middlesbrough striker Bradley Fewster netted a hat-trick, with Blackburn Rovers forward Dean Rittenberg scoring the other goal for the hosts.
Gray's Blues team-mate Reece Brown failed to make the matchday 16 today, although he will be hoping to play some part in England U18s upcoming double-header against Croatia.
A number of Blues staff were in attendance to watch Gray in action, including Blues Academy coach Steve Spooner who felt Gray performed well on his first start.
"In the first half in particular, Dimmi put in some good crosses," he said.
"His play was neat and tidy, he worked hard and he can be pleased with how well he did."
England U18s (4-3-3): 1 Ted Smith (Southend United); 2 Kyle Knoyle (West Ham United; 12 Ben O'Hanlon (Wolverhampton Wanderers) 65), 5 Reece Burke (West Ham United), 6 Brendan Galloway (MK Dons), 3 Ben Chilwell (Leicester City); 4 Bryn Morris (c; Middlesbrough), 8 Harry Winks (Tottenham Hotspur), 10 William Miller (Tottenham Hotspur; (14 Alex Gilliead (Newcastle United) 85); 7 Demarai Gray (Birmingham City), 9 Bradley Fewster (Middlesbrough; 15 Dean Rittenberg (Blackburn Rovers) 72), 11 Nathan Oduwa (Tottenham Hotspur).