Patrick Mahomes led a thrilling late comeback as the Kansas City Chiefs ended their 50-year wait for a Super Bowl crown with a 31-20 victory over the San Francisco 49ers on Sunday.

Chiefs quarterback Mahomes shrugged off an error-strewn start to the game to overturn a 20-10 fourth-quarter deficit in a nail-biting contest at Miami's Hard Rock Stadium.

The Super Bowl win was Kansas City's first NFL Championship since their triumph over the Minnesota Vikings in 1970.

And it owed everything to the nerve of Mahomes, who for the third straight game led the Chiefs back from a double-digit deficit to seal the victory.

"We never lost faith. Everybody on this team, no one had their head down and we found a way to win in the end," Mahomes told a television reporter as cannons blasted confetti into the Florida night sky.

The Chiefs quarterback had looked out of sorts through the first three quarters, throwing two interceptions in the face of fierce pressure from the magnificent San Francisco defence.

But with the game on the line in the fourth quarter, Mahomes led his team on two long drives to set up touchdowns for tight end Travis Kelce and running back Damien Williams.

Those scores put the Chiefs into a 24-20 lead and Kansas City made the game safe when Williams danced up the sideline for a 38-yard rushing score with 1min 12sec remaining.

Mahomes finished with 286 passing yards and 26 completions from 42 attempts with two touchdowns. The Chiefs quarterback also rushed for a touchdown early in the first quarter.

But the defeat was desperately hard on the 49ers, who were chasing a record-equalling sixth Vince Lombardi Trophy.

The 49ers had barely put a foot wrong through three quarters, with their defence shackling Mahomes superbly and their offence moving the ball confidently to put them in the driving seat late in the game.

But as the pressure in the fourth quarter mounted, 49ers quarterback Jimmy Garoppolo's sure touch deserted him and the Niners offence dried up.

The fourth-quarter collapse was also 49ers coach Kyle Shanahan's worst nightmare.  Shanahan had been the offensive coordinator for the Atlanta Falcons at the 2017 Super Bowl when they let a 28-3 lead slip in a stunning loss to the New England Patriots.