``We just didn't play very well,'' said coach Phillip Fulmer, whose team joined the national championship race with a 34-32 victory over Florida last week. ``We got here together. We lost together.''
Mauck, a 22-year-old freshman who spent three years as a catcher in the Chicago Cubs' organization, put LSU ahead for good with a 13-yard touchdown on the second play of the fourth quarter. He also scored LSU's first TD on a 4-yard run.
Another backup, Domanick Davis, finished off the Vols by diving over the top on fourth-and-goal from the 1 with 2:26 remaining.
Tennessee could have made things a little easier on the BCS by winning. But the Vols couldn't beat an LSU team that lost both Davey and star running back LaBrandon Toefield to injuries in the first half.
LSU (9-3) earns a spot in the Sugar Bowl against No. 8 Illinois with a truly remarkable upset, the final surprise in a regular season that ended a week later than expected because of the Sept. 11 terrorist attacks.
Nebraska, Florida and Texas all fell by the wayside in recent weeks. Now, Heisman Trophy winner Eric Crouch and the Cornhuskers might be back in the picture, getting a chance to play for the national title when they didn't even win their own division in the Big 12 Conference.
After falling behind 17-7, LSU held the Vols to a field goal in the second half.
Travis Stephens, who rushed for a career-high 226 yards in the upset of Florida, managed just 37 yards on 14 carries. He also had a crucial fumble that led to Mauck's go-ahead touchdown.
Kelley Washington had six catches for 103 yards in the first half but just three for 37 yards over the final two quarters.
Down 24-20, the Vols had a chance after a short punt gave them the ball near midfield. Casey Clausen completed a 17-yard pass over the middle to Donte Stallworth, but Demetrius Hookfin stripped the ball and Ryan Clark recovered the fumble for LSU.
LSU then drove 65 yards for the clinching score. Appropriately, Mauck and Davis did all the running for the Tigers, while the Vols made two more crucial mistakes.
Julian Battle had an interception right in his hands but couldn't hang on. Rashad Baker tripped up LSU's star receiver, Josh Reed, and was penalized for interference.
Toefield, who tied an SEC record with 19 rushing touchdowns, went out with an injured left knee. He gained just 18 yards.
But Davis ran for 78 yards and Mauck contributed 43 yards on the ground, usually taking off from the shotgun. Mauck completed just 5-of-15 passes for 67 yards, but was named the MVP.
Tennessee's last hope died when Stallworth, trying desperately to pick up a first down, was dragged down by four tacklers at midfield with a minute to go.
On LSU's second possession, Davey was leveled by Tennessee linebacker Keyon Whiteside at the end of a 2-yard run. The quarterback appeared to be out of bounds when Whiteside drove his helmet into Davey's left ribs, but no penalty was called.
After several minutes on the turf, Davey finally managed to walk slowly to the locker room for X-rays. Nothing was broken, and he returned to the field for LSU's next series.
In the meantime, Mauck guided the Tigers to the end zone, taking advantage of three Tennessee penalties. The Vols were twice called for being offsides on incomplete passes, and a flag was thrown for pass interference when Reed was tripped up near the goal line by Baker, an omen of things to come.
Davey took another shot in the ribs just before the end of the first half and didn't return. That brought on Mauck, who had played only two games and thrown just 26 passes in his career.
He wound up making a Mauck-ery of the BCS.
For a while, it seemed as though things would work out for Tennessee, which wiped out an early 7-0 deficit with 17 straight points in the second quarter.
Clausen threw a perfectly placed pass to Washington for a 31-yard touchdown with 9:04 left in the half. The quarterback simply threw to the goal line and Washington ran under the ball at the left pylon without breaking stride.
The Clausen-to-Washington combination worked again on Tennessee's next possession, this time for 47 yards to set up a 3-yard touchdown pass to fullback Troy Fleming.
Hoping to turn the momentum, LSU coach Nick Saban gambled on fourth-and-inches at the Tigers 22. The plan backfired when Davey, attempting a sneak, fumbled the snap and was wrapped up by Demetrin Veal for no gain.
Tennessee actually went backward — Clausen was called for intentional grounding — but Alex Walls equaled the longest field goal of his career when he connected from 51 yards.
LSU got to 17-10 at halftime when John Corbello made a 45-yard field goal. In the third quarter, he hit from 47 and 45 yards to pull the Tigers within 17-16.
Reed and Stephens both set records.
Reed had four catches for 60 yards, giving him 3,001 in his career. He broke the SEC mark of 2,964, set by Boo Williams of Vanderbilt from 1985-88.
Stephens wound up with 1,464 yards for the season, eclipsing Jay Graham's 6-year-old school record of 1,438.