With 1:26 left in the game and Tennessee (10-4) up by four points, Wisconsin began driving the field as Donovan completed consecutive passes of 21, 10 and 13 yards and drew the Vols offsides for 5 penalty yards.
On first down and 5 yards to go at the Tennessee 36, Donovan threw down field to Paul Hubbard.
"I just knew I had to go to the highest point and make a good catch," said Wardlow, who returned the pick for 16 yards with 28 seconds left in the game.
The Vols defense allowed Wisconsin (9-5) 203 yards on offense in the second half but held the Badgers to only a field goal as the Tennessee offense failed to get in the end zone.
The Vols also managed to pressure Donovan, who left the game for a few snaps in the second quarter after taking a hard hit from linebacker Jerod Mayo, who led Tennessee with 13 tackles.
"In the second half, our defense, bowing its neck like it did, was incredible," Tennessee coach Phillip Fulmer said. "They basically preserved the win for us."
The Vols defense has come a long way from the first half of the season, when it couldn't stop opponents from piling up yards and recording career statistics against them.
The Vols held Wisconsin tight end Travis Beckum, whose 960 yards receiving led the nation for tight ends entering the Outback Bowl, to only 22 yards on two catches.
Tennessee also sacked Donovan three times -- the same total the Vols recorded in their first seven games put together -- for a total loss of 16 yards.
"We knew if we pressured Donovan he'd get a little rattled and we hurt him, and I didn't think he wanted to play very much after the first two quarters," linebacker Ryan Karl said.
Tennessee defensive coordinator John Chavis said he saw his squad change after a strong outing against Georgia, when the Vols gave up only 14 points and shut down a formidable Bulldog rushing attack.
Chavis said the defense struggled early in the season because of the inexperience of young players who were forced to fill in for injured teammates.
"It wasn't because of the lack of effort," he said. "We had a lot farther to go than any (team) that I've ever been around." The players said they grew up by focusing on correcting their mistakes and bonding as a team.
But more importantly, Chavis said, they learned to be resilient in the face of tough losses and heavy criticism from the fans.
"They had the tombstone put up for us," he said. "The grave was there, but we didn't fall in."
