The Peterborough Lakers lost an intense 11-9 battle with the Brooklin Redmen on the road meaning the series is now knotted at two games apiece.
Curtis Dickson scored to get the Lakers within a goal late in the game but a last-minute goal by Austin Shanks sealed the win.
Game 5 will go Monday night at the Memorial Centre.
In the other semi-final, Oakville stunned Six Nations 10-5 to tie their series at 2.
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