Nico Rosberg made history as the first Formula One driver to set a timed lap at the inaugural Russian Grand Prix on Friday but championship leading Mercedes team mate Lewis Hamilton still ended up on top.
Rosberg set a best time of one minute 42.311 seconds around the Sochi circuit, which snakes past some of the landmark venues used at this year's Winter Olympics, in a sunny morning session with Hamilton second.
The Briton, who leads Rosberg by 10 points after winning the last three races, went top of the timesheets in an interrupted afternoon session with a best of 1:39.630.
The red flag came out eight minutes from the end when Australian Daniel Ricciardo's Red Bull halted with a power unit failure.
Mercedes are expected to wrap up the constructors' championship on Sunday with three races to spare, having won 12 of the 15 so far with eight one-two finishes.
Hamilton, the 2008 champion, is chasing his ninth win of the season.
Ferrari's Fernando Alonso was the first driver out of the pit lane when the green light came on, leading Force India's Nico Hulkenberg.
McLaren's Jenson Button was the early pacesetter as drivers got to grips with a layout compared to the former Valencia street circuit and Singapore, with the 2009 champion ending the morning as the third fastest.
He also collected two fines totalling 1,100 euros ($1,391.72) for pitlane speeding and was sixth fastest in the second session.
Alonso was fourth and third in the two sessions, with Danish rookie Kevin Magnussen, Button's team mate, fifth and then second in the afternoon.
The only Russian regular, Toro Rosso's 20-year-old rookie Daniil Kvyat, followed up seventh in the morning with eighth after lunch.
That was still ahead of both Red Bulls, his 2015 employers, with four times champion Sebastian Vettel ninth after reporting a loss of power on the straight and Ricciardo 13th.
He was joined for the first session by 19-year-old compatriot Sergey Sirotkin, making his debut at a race weekend in the Sauber usually driven by Mexican Esteban Gutierrez.
Williams had a disrupted opening session when a problem with a tyre blanket damaged a set of Valtteri Bottas's tyres, limiting his running.
All drivers took to the track with stickers of support for Jules Bianchi, Marussia's French driver who was severely injured in a crash in Japan last Sunday and remains in critical condition.
Marussia announced before the session that they would have only one car running this weekend, with Bianchi's assembled and left in the garage as a mark of respect.
Chilton ended the first session with the slowest time but picked up speed in the afternoon.
"I don't know how to put into words how truly devastated I am by what has happened to Jules," he had said before the session started.
"It is going to be a very emotional weekend for the whole team, but we will try to get through it and keep praying for Jules."