Former champion Nico Rosberg has warned George Russell of the "ultimate challenge" that lies ahead after finishing ahead of Lewis Hamilton this season.
Russell lined up alongside Hamilton at Mercedes for the first time this year after replacing Valtteri Bottas.
Despite a difficult start as Mercedes dealt with the effects of porpoising, Russell recovered to score the team's only win of the year at the São Paulo Grand Prix.
The Silver Arrows had experimented with split set-ups between its two drivers to combat its fundamental issues with the W13, with Russell coping best with a stunning run of top-five finishes that was only broken with a retirement at the British Grand Prix.
The performances culminated in him finishing 35 points ahead of Hamilton to complete a feat only previously matched by Jenson Button at Mclaren and Rosberg, who beat the Briton to the 2016 title.
But the German believes the scenario would have played out differently had Mercedes been competitive from the start of the year.
"It would still be a different situation if then next year they start right at the front, fighting for podiums and wins from the get-go, being away from all the mess of the pack," Rosberg told Sky Sports' Any Driven Monday.
"That will still be a different situation where they are not completely lost and they don't know what is going on with the set-up and have to try everything.
"So George has to prove it again next year and see if he can stay ahead of Lewis.
"That is the ultimate challenge."