Clausen came off the bench when starter Erik Ainge was injured midway through the second quarter with the Vols behind by three touchdowns. Clausen rallied Tennessee with a touchdown pass and a 1-yard TD sneak that made it 24-14 with 9 minutes, 35 seconds left in the fourth quarter.
He finished 21-for-32 for 196 yards and appeared to settle the Vols' quarterback controversy.
"Getting done what he got done, coming back here to win this football game at a place where he had been, I don't know if there is a better story in the world than what this guy has done," Tennessee coach Phillip Fulmer said.
The Tigers (1-1, 0-1) had first crack in overtime, but managed only a 31-yard field goal by Colt David.
Riggs accounted for all the Vols' yards in overtime with a 10-yard reception and four runs. He powered through the line and in for the game-winner on second down.
"I don't know what happened out there. We played like a joke out there in the second half," LSU defensive tackle Kyle Williams said.
Hurricane Katrina forced the No. 4 Tigers to postpone their first home game, and move their second to Arizona State, where LSU came away with a dramatic win.
Then Hurricane Rita created another delay and set up the first Monday nighter in Tiger Stadium.
* Vanderbilt wide receiver George Smith was shot in the arm and two teammates were injured over the weekend at a party at a university apartment building, a school spokeswoman said.
Smith, a redshirt freshman, was shot in the arm early Sunday by someone who is not a university student, school spokeswoman Melanie Moran said. He was taken to Vanderbilt hospital, was treated and released.
Freshman defensive end Derrius Dowell and redshirt freshman safety Reshard Langford sustained minor cuts and were also treated and released.
* Southern Utah's game at McNeese State on Saturday has been postponed indefinitely because of Hurricane Rita. McNeese State is located in Lake Charles, La., which was directly in the path of the storm.
* Memphis quarterback Will Hudgens broke his right leg in last weekend's game at Tulsa, 3 weeks after the Tigers' original starter broke his leg in the opener. Hudgens broke his fibula and damaged a ligament late in the fourth quarter in the 37-31 overtime loss Saturday night, the team said.
Hudgens became the starter after Patrick Byrne broke his right fibula and tibia against Mississippi on Sept. 5. *