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SHANGHAI (AP) — Four-time world champion Sebastian Vettel isn't used to being asked to step aside for a teammate. Now it's happened twice in two races.

Vettel, only months removed from wrapping up his most dominant season in F1, was instructed by his team to allow debutant teammate Daniel Ricciardo to pass him midway through Sunday's Chinese Grand Prix as the German's speed began to fade due to his rapidly degrading tires.

The German initially fought off Ricciardo's attempts to get by and testily asked his team which tires the Australian was using. When told both drivers were on medium tires, Vettel responded over the radio, "Tough luck."

He did finally accede, but his initially defiant response raised questions after the race whether there was discord simmering in the Red Bull camp.