While Brian McDermott's team have nothing but pride to play for, their opponents are a point behind Hull in the battle for automatic promotion and must avoid defeat to stand a chance of finishing in the top two.
Tonge, who has appeared in every game since McDermott replaced Neil Warnock in the Elland Road hotseat, realises his side will be underdogs but believes they can make Saturday afternoon a tense one for the Hornets.
"It's going to be a tough game for us with their situation," Tonge told Leeds' official website.
"They will be nervous, I don't think they would be human if they weren't. Obviously if Hull win they will be promoted, but Watford won't want Hull to get beat and not have taken advantage of that.
"They will be up for the game I'm sure, but when there is so much riding on it I'm sure they will be nervous so hopefully we can take advantage of that."
The former Sheffield United midfielder also insisted that the Whites would not take to the field with one eye on their end-of-season holidays.
He added: "We will be professional and approach it like every other game this season. We want to win and do well.
"Everyone has a point to prove and is playing for places. There is no easing off because it's the last game of the season. We'll be going out to try and get three points."