Valtteri Bottas emerged from Friday's Russian Grand Prix opening practice 0.211 seconds quicker than Lewis Hamilton for a Mercedes 1-2 at the Sochi circuit in the former Olympic Park.
Red Bull's Max Verstappen, who leads Hamilton by five points in the world championship, came in third, just 0.16 sec behind his title rival.
With a penalty after being deemed "predominately" to blame for his Monza crash with Hamilton, the best Verstappen can hope for on Sunday's grid is fourth.
Sochi has proved a fertile hunting ground for Hamilton, who is targeting a fifth win in Russia to seal an unprecedented century of wins.
The seven-time world champion has been stuck on 99 since the British Grand Prix at Silverstone.
Ferrari's Charles Leclerc took fourth in the morning session. The man from Monaco will start from the back of Sunday's grid after an engine change.
Red Bull could choose this 15th round of the championship to fit Verstappen's car with a new engine as well to see it through to the end of the season.
In fifth and sixth came Sebastian Vettel, who announced this week he is staying at Aston Martin next year, and Alpha Tauri's Pierre Gasly.
A routine session for most of the drivers apart from McLaren's Lando Norris who crashed on the way back to the pits.
"I don't know what happened, the rear just locked," said the Briton who is lying fourth in the championship standings.
One man happy to be back on the track despite only posting the 15th fastest time was Kimi Raikkonen after the Alfa Romeo driver missed the last two races following a positive Covid-19 test.
The session was blessed with sunshine but heavy rain is forecast for Saturday's qualifying.