Harper made four consecutive free throws over the final 31 seconds and two late 3-pointers to help Auburn clinch an 84-80 victory over No. 5 Tennessee on Saturday in the regular-season finale.
The Tigers (22-9, 11-7 Southeastern Conference) collected their fourth straight win and biggest of the season in a packed Auburn Arena. It was Auburn's first victory over a team ranked in the top five since beating Arkansas in 1995.
"Everybody in the country recognizes that Tennessee is a Final Four team," said Auburn coach Bruce Pearl, a former Tennessee head man. "Everybody in the country now recognizes that Auburn is capable of beating and, in fact, did beat a Final Four team."
The Volunteers (27-4, 15-3) could have clinched at least a share of the SEC regular-season title with a win, but they now need No. 10 LSU to lose later Saturday to Vanderbilt, which is winless in league play.
Tennessee has never won back-to-back league crowns, and the loss ensures LSU will be the No. 1 seed for the SEC tournament.
"A year ago, you think about it, we win the league with five losses," Tennessee coach Rick Barnes said. "This year we only have three. You have to learn from this. Some of the mistakes we made today, we can't make. Not at this time of year."
The two teams shared the SEC regular-season title last season, and Auburn spent six weeks ranked in the top 10 before falling from the rankings.
Auburn relished the spoiler role this time. The Tigers will be the No. 5 SEC seed and receive a first-round bye in the league tournament.
With under two minutes to play Saturday, Auburn's Samir Doughty grabbed the ball after Grant Williams' shot was blocked and made a 3-pointer to beat the shot clock. Harper hit two free throws with 31 seconds left for an 80-74 cushion, and Jordan Bone's 3-point attempt at the other end didn't fall.
Williams got the rebound and drew a flagrant foul 1 from Anfernee McLemore. Williams made two free throws with 23 seconds left and the Vols got another possession. Williams launched a quick basket off the inbounds play.
But Harper hit two more free throws with 20 seconds left for an 82-78 lead. He had sealed Tuesday night's 66-60 victory at Alabama with two late drives to the basket.
"He just has had four great games," Pearl said. "In many ways, put the team on his back, accepting the responsibility of a quarterback to have to make plays. He's been exceptional."
Bone then missed a 3-point try and teammate Jordan Bowden couldn't control the rebound, which went out of bounds.
Doughty hit two more foul shots for the Tigers. They celebrated moments later, with Bryce Brown climbing on the press row table in front of the student section after his final home game.
"That's something I just planned to do," said Brown, who had 16 points and four 3-pointers. "I just wanted to share the moment with the fans. I wanted to share the moments with my parents. My auntie and my mom were up there, that's who I went to."
Chuma Okeke led Auburn with 22 points, one shy of his career high. Harper had 16 points and eight assists, with his only two 3-pointers coming back to back in the final minutes.
Williams finished with 25 points and nine rebounds for the Vols. Bone had 17 and Bowden 16. Admiral Schofield scored 13 before fouling out.
"We won the game, Tennessee didn't lose it," Pearl said. "We won the basketball game because of the quality of our play."
Tennessee: A 28th victory would have tied for second-most in program history. The Vols' four losses have come by a combined 29 points. They outrebounded Auburn 39-27.
Auburn: Finished regular season 2-5 against ranked opponents. Had perhaps its best all-around performances of the season, committing only five turnovers.
Harper's second 3-pointer in the final minutes appeared to have been tipped in by McLemore.
"It should have been a 2-point play," Barnes said. "That's what everybody's told me since I walked in."
He didn't get any argument from Harper. "I thought Anfernee tipped that in, honestly," the Tigers point guard said.
Tennessee gets a double bye before opening SEC tournament play in Nashville, Tennessee.
Auburn opens the SEC tournament Thursday hoping to improve its NCAA tournament seeding.
The Associated Press contributed to this report.
Marquis Weddle's and-1 helps Jackson TN Underdawgs pull off upset
Marquis Weddle gets the tough and-1 to go which is the big bucket in Jackson TN Underdawgs' upset of House of 'Paign.
Top-5 projections for the 2021 NBA draft
Mike Schmitz joins SportsCenter to discuss the measurables of the players expected to be picked in the top five in the NBA draft.
UConn Huskies men's basketball says probation over NCAA violations under Kevin Ollie now over
The two-year probation imposed on UConn for NCAA violations under former coach Kevin Ollie has ended.