Patrick Mahomes, Travis Kelce and the Kansas City Chiefs are back-to-back Super Bowl champions - now they are targeting a three-peat.

Mahomes threw a three-yard touchdown pass to Mecole Hardman with three seconds left in overtime as the Chiefs rallied to beat the San Francisco 49ers 25-22 on Sunday (Monday AEDT).

Victory made Kansas City the first repeat Super Bowl champions in 19 years, and the ninth overall.

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

"The goal has always been to get three," Kelce said on stage after sharing a kiss with Swift.

"But we couldn't get here without getting that two, and having that target on our back all year ... how about that.

"We get a chance to do it three times in a row."

The NFL's first Super Bowl in Las Vegas was a sloppy, mistake-filled affair that lack excitement until the back-and-forth final quarter and overtime.

It was the second of 58 Super Bowls to be tied after regulation time, and the first played using the 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 Mahomes rallied his side.

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.

"With all the adversity we've been through this season to come through tonight ... I'm proud of the guys," said Mahomes, who earned his third Super Bowl MVP award.

"This is awesome. Legendary."

The action picked up after a crucial blunder by San Francisco's special teams set up Mahomes' 16-yard touchdown pass to Marquez Valdes-Scantling for a 13-10 lead.

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

"We have the offence to score touchdowns and I failed to put the team in position to do that," Purdy said.

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 - the most recent team to go back-to-back following the 2003 and 2004 seasons.

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

"I am going to celebrate tonight, celebrate at the parade and then work my way to get back in this game next year," Mahomes said.

"I am going to do whatever I can to be back in this game next year. Three-peat."

After Moody's 53-yard field goal gave the 49ers a 19-16 lead with one minute and 53 seconds remaining, Mahomes and Kelce went to work.

Mahomes connected with Kelce for a 22-yard gain to set up Harrison Butker's tying kick, a 29-yarder with three seconds left to send the game to overtime.

The rest is history.