Chatham fell behind early Sunday night in game 3, before dropping a 7-6 decision in overtime.
Steven Beenackers scored twice for the Maroons, while Jake O’Donnell, Teddy McGeen, Brendan D’Agostino, and Alec MacKenzie also scored for Chatham.
Brendan Johnston made 35 saves in the loss, Chatham’s second straight game allowing 7 goals to London.
Local product Kyle Dawson scored for the London Nationals in the win.
Game four is Wednesday in London, while game five will be back in Chatham Thursday at 7pm.