Ellis Taylor scored twice for the hosts at Eppleton CW, with his first coming from the penalty spot, before a stunning strike six minutes before half time.
Lee Burge started in goal for Sunderland while three trialists also featured in the Premier League 2, Division 2, clash.
The Black Cats have one league game remaining this season and will face Southampton next week.
Here’s how each player fared for the hosts against Birmingham:
1. Lee Burge - 7
Could do little about the goal. Made a few important saves to keep his side ahead at the end of the first half. 7 Photo: JPI Media
2. Joe Littlewood - 6
Won a few early defensive duels at right-back but was beaten a few times towards the end of the first half. Was substituted early in the second half. 6 Photo: Getty Images
3. Xavier Benjamin - 6
On trial from Fulham. Took a few chances in possession but showed his physical presence in the heart of Sunderland’s defence. 6 Photo: JPI Media
4. Cameron Jessup - 7
Won the majority of his headers at the back and produced some important challenges. 7 Photo: JPI Media