Givani Smith scored the go-ahead goal 8:03 into the third period as Kitchener topped the Sting 5-3 to tie their second-round playoff series at two games apiece.
Kole Sherwood, former Spitfire Austin McEneny, Jonathan Yantsis and Connor Bunnaman also scored for the Rangers, who host Game 5 tonight.
Connor Schlichting, Brayden Guy and Jordan Kyrou scored for Sarnia.
In other OHL action, former Spit Gabriel Vilardi scored twice as Kingston downed the Colts 7-1 to take a 3-2 lead in their series.
Max Jones, Brett Neumann, Jason Robertson, former Spit Sean Day and Matt Hotchkiss also scored for the Frontenacs, who will host Game 6 tonight.
Robert Thomas had a goal and an assist as the Hamilton Bulldogs advanced to the Ontario Hockey League conference final by doubling up Niagara 4-2 in Game 5 of their second-round series.
The Bulldogs will face the winner of the series between the Barrie Colts and Kingston Frontenacs.