The Kansas City Chiefs, defending Super Bowl champions, suffered their first loss of the NFL season on Sunday, falling 30-21 to the Buffalo Bills after winning their first nine games.

The result ends any talk of the Chiefs matching the 1972 Miami Dolphins team with a perfect, unbeaten season and was another reminder of the class of the Bills and their quarterback, Josh Allen.

With the Bills leading 23-21, Allen secured the victory in stunning fashion with a 26-yard rush on fourth down and two, demonstrating not only his footwork and speed but also his strength as he broke two tackles to power into the end zone.

"We had a man play, they dropped out into zone, they had something good for it," Allen said. "I'm just trying to make a play, help our team win a football game."

"There are some things we want to clean up, some throws I wish I had back," he added. "But we're going into the bye week 9-2 – we'll take it. Knowing how things usually play out, we'll probably see this team again at some point."

While the Bills have beaten Kansas City in each of the past four NFL seasons, the Chiefs have eliminated the Bills from the playoffs in three of the past four seasons.

The Bills opened a 23-14 lead early in the fourth when Allen found Curtis Samuel with a 12-yard touchdown pass.

Patrick Mahomes responded though, finding Noah Gray with a one-yard pass to make it a two-point game.

Then came Allen's inspired touchdown run, which left Mahomes in need of one of his famous comebacks. But on fourth down, his pass intended for Travis Kelce was intercepted by Buffalo's Terrel Bernard. (AFP)