Valtteri Bottas will partner Lewis Hamilton for another year at Mercedes under a new contract which allows the Formula One team to keep their options open for 2019.
The one-year deal announced Wednesday was expected after two victories this season by Bottas and a harmonious partnership with three-time champion Hamilton.
The 28-year-old Finnish driver had joined Mercedes on a one-year contract in January as a replacement for retired world champion Nico Rosberg, whose relationship with Hamilton had soured amid fierce rivalry.
After 13 races with the team, Bottas is third in the drivers' standings behind Hamilton and Ferrari's Sebastian Vettel.
He has enjoyed victories in Russia and Austria, his first wins in F1, with nine podium places and two pole positions, after previously racing in F1 for four years with Williams.
"Overall, the balance of his performances and his upward trajectory made it a no-brainer for us to continue with him into 2018," Mercedes motor sport chief Toto Wolff said on the team's website:
With Hamilton's current contract also running until 2018, Mercedes appears to be keeping their options open, with Red Bull drivers Daniel Ricciardo and Max Verstappen also holding contracts which run until the end of next year.
Rivals Ferrari had already extended the contracts of Vettel, until the end of 2020, and Raikkonen, for another year.
Hamilton said at the end of last month he planned to extend his contract but said there was no hurry on talks.
Wolff indicated the dynamics between Bottas and Hamilton had played a part in the team's decision.
"For our team, the bonus factors are the respect and sportsmanship that have grown between our two drivers," he said.
"The chemistry and dynamic between Valtteri and Lewis work and are what we need to take the fight to our competitors."
Bottas said: "When the team hired me for the 2017 season, they took a leap of faith by putting their trust in my skills.
"This new contract shows that I've earned that trust."