LAS VEGAS — Patrick Mahomes, Travis Kelce, and the Kansas City Chiefs are back-to-back Super Bowl champions.

Mr. Mahomes threw a three-yard touchdown pass to Mecole Hardman with three seconds left in overtime, and the Chiefs rallied to beat the San Francisco 49ers 25-22 on Sunday in the second overtime game in Super Bowl history, becoming the first repeat champs in 19 years and ninth overall.

With pop star Taylor Swift watching her boyfriend Mr. Kelce from a suite, the Chiefs captured their third Super Bowl title in five years and firmly established themselves as a dynasty.

The overtime win followed a first half filled with miscues by the defending Super Bowl champions before the Chiefs took their first lead with a third-quarter touchdown — to Ms. Swift’s delight — only for the Niners to regain a three-point advantage early in the fourth.

The NFL’s first Super Bowl at Las Vegas was a sloppy, mistake-filled affair that was mostly uneventful until the back-and-forth fourth quarter and overtime. It was the second of 58 Super Bowls to be tied after regulation, and the first played under new overtime rules under which both teams got the ball.

The Chiefs trailed 22-19 after Jake Moody kicked a 27-yard field goal on the first possession of overtime, but Mr. Mahomes rallied the Chiefs, completing another impressive comeback in a rematch of a Super Bowl four years ago.

Mr. Mahomes ran eight yards on fourth-and-one to keep the Chiefs’ chances alive and then scrambled 19 yards to set up the winning score.

After he connected with the wide-open Mr. Hardman, the Chiefs ran on the field as red-and-yellow confetti fell onto the turf.

The most excitement in the first half came when a frustrated Mr. Kelce bumped Andy Reid on the sideline, knocking the Chiefs’ 65-year-old coach a few steps back after teammate Isiah Pacheco fumbled inside the red zone during the second quarter.

The action picked up after a crucial blunder by San Francisco’s special teams set up Mr. Mahomes’ 16-yard touchdown pass to Marquez Valdes-Scantling for a 13-ten lead.

Quarterback Brock Purdy and the 49ers answered but they couldn’t make enough plays, denying the so-called Mr. Irrelevant an opportunity to go from last pick in the 2022 NFL draft to Super Bowl champion.

Messrs. Mahomes and Reid are now halfway to Tom Brady and Bill Belichick, who won six championships in 20 years together with the New England Patriots and were the most recent team to go back-to-back following the 2003-2004 seasons.

The 28-year-old Mahomes becomes the fourth starting quarterback to win three Super Bowls — joining Mr. Brady, Joe Montana, Terry Bradshaw, and Troy Aikman — and the second-youngest.

Niners wide receiver Jauan Jennings threw a touchdown pass and caught one, joining Eagles quarterback Nick Foles six years ago as the only players to do both in the Super Bowl.

After Mr. Moody’s 53-yard field goal gave the 49ers a 19-16 lead with 1:53 remaining, Messrs. Mahomes and Kelce went to work. Mr. Mahomes connected with Mr. Kelce for a 22-yard gain to set up Mr. Butker’s tying kick, a 29-yarder with three seconds left.

A holding call on Kansas City’s Trent McDuffie extended San Francisco’s opening drive of overtime and Mr. Purdy made key throws to drive the 49ers to the Chiefs nine. San Francisco, though, settled for a field goal.

For the game’s halftime show, R&B star Usher emerged seated on a throne, joined by a marching band and a trove of Vegas performers — but stayed its center.

It was an immediate confirmation of his position as the ideal halftime performer: one with timeless, well-known hits, masterful choreography, and a devoted audience.

He started with “Caught Up,” moving into “U Don’t Have to Call,” “Superstar,” and “Love in the Club.”

Then Alicia Keys joined in front of bright red piano for her song “If I Ain’t Got You,” which morphed into “My Boo,” Usher losing a glove in an apparent tribute to Michael Jackson — notable for a performance during Black History Month.

“They said I wouldn’t make it,” he told the crowd, dedicating the set to his “mama.”

Across 13 minutes during the halftime show sponsored by Apple Music, Usher brought out a number of guests including H.E.R., Jermaine Dupri, Lil Jon (for “Turn Down for What,” which became “Yeah!” — and included a guest appearance from Ludacris).

Across three decades, Usher had an endless treasure trove of hits to pull from — and did so with costume changes, and a rolling performance of “OMG” while wearing roller skates — at one moment, sliding between will.i.am’s legs.

His album “Confessions” ranks among one of the best-selling music projects of all time and turned 20 this year; “Burn” became an easy performance highlight.

Ms. Swift was among the throng attending Sunday’s game at Allegiant Stadium, strolling in surrounded by celebrity friends. She cuddled with Blake Lively during Post Malone’s performance of “America the Beautiful” and won what appeared to be a beer chugging contest, slamming her cup down to an appreciative roar from the fans.

The pop superstar completed her trip to Las Vegas from the Tokyo Dome for the game, walking through security along with Ms. Lively, Ice Spice, and her mother, Andrea Swift. 

Ms. Swift later was spotted talking to Mr. Kelce’s brother, Philadelphia Eagles center Jason Kelce, and the NFL commissioner, Roger Goodell, in one of the private boxes that reportedly cost more than $1 million. Singer Lana Del Rey joined the celebrity-packed suite in time to catch Usher’s halftime show.

Ms. Swift, who has been dating Mr. Kelce since the first few weeks of the NFL season, flew on a private plane across nine time zones and the international date line from the last of four shows at the Tokyo Dome in Japan to arrive about two hours before kickoff. The time change allowed her to land at Los Angeles and make the final hop to Las Vegas.

The 14-time Grammy winner walked in wearing a black outfit with a red jacket slung over her shoulder, apparently getting the memo from Mr. Kelce and many of the Chiefs. 

Mr. Kelce wore a shimmering black suit, quarterback Patrick Mahomes wore a sharp black suit of his own, and even the Chiefs coach, Andy Reid, wore a black blazer as the Chiefs appeared to lean into the role of the villains.