The Rockhoppers deservedly led 8-5 after three periods. But it all went wrong for them in the last as Birmingham scored five times without reply through Fleur Kennedy (2), Lauren Keight, Claire O'Sullivan and Chloe Arthur to win 10-5.
It's tight at the top, with Devonport and Liverpool Water Beatles also completed fifth straight victories. Samantha Capparilli scored five of Devonport's goals in a 12-8 defeat of Southampton; Liverpool's youngsters outplayed Iceni 14-1.