The LaSalle Vipers will be facing elimination when they take on the Nationals Wednesday night at Western Fair in London.
The Nationals grabbed a commanding 3-1 series lead Tuesday at the Vollmer Centre with a 6-2 victory.
James Turner scored twice and Isaiah Payne had the game-winner for the Nationals.
Jack Bowler and Zane Dalpe scored for the Vipers.
Goalie Will Tragge made 22 saves in the loss.
Also Leamington now trails its series with the Kings 3-1 after losing 5-2 Tuesday night in Komoka.
Game five in that Greater Ontario Junior Hockey League series is set for Thursday night in Leamington.