Red Bull chief Christian Horner said it would be "almost impossible" for his team to better this season's performance after they won Formula One's constructors' championship on Sunday.

Max Verstappen romped home to win the Japanese Grand Prix and give Red Bull an unassailable lead in the standings with their 15th victory in 16 races this season.

Their lead over second-place Mercedes is now so big that they were able to clinch the title even though Verstappen's teammate Sergio Perez retired from the race.

Runaway championship leader Verstappen has been in imperious form with 13 victories this season, while Perez has chipped in with two.

Defeat at last week's Singapore Grand Prix ended Red Bull's hopes of an unprecedented unbeaten season and Horner thinks what they have achieved may never be repeated.

"It's a golden moment -- for the team to do better than we're doing I think it's almost impossible," he said.

"We're riding a wave and of course we want to try and ride that wave as long as we can, but Formula One is a fast-moving business.

"We see how quickly teams move up and move down."

The win gave Red Bull their second straight constructors' championship and put Verstappen within touching distance of his third consecutive driver's title.

Horner said the Dutch driver was "at the top of his game".

"I think he's just got this inner hunger and determination and huge ability," he said.

"He channels it, he doesn't get distracted by some of the trappings of Formula One -- he's just an out-and-out racer."

Horner had sympathy for Perez, who retired early in the race, telling his team "the car doesn't feel right".

Perez had already picked up two penalties by then and later came back out onto the track to ensure he would not have to serve them at next month's Qatar Grand Prix.

"I think this is a big confidence circuit," said Horner.

"Where Sergio was struggling was mainly in the high-speed corners compared to Max.

"You could tell with Max, the confidence that he had, the speed that he was able to carry through the high-speed stuff was mind-boggling."

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