Max Verstappen posted the fastest lap time during the second practice session in Russia, as championship leaders Mercedes struggled.
Red Bull come to Sochi off the back of tough run of results where, due to first-lap collisions and grid penalties for changing engine components, it has only had one podium in the last three races.
The Milton Keynes-based outfit’s hopes of repeating its third place finish from Singapore has been dampened by an ICE change on both Verstappen and Alex Albon’s car, which will see the pair incur five-place grid penalties.
Although Mercedes boast a 100% win record at the Sochi Autodrom, Ferrari is the form team at present as it aims to extend its run of three victories into four for the first time since 2008.
Both Ferrari and Mercedes chose to run the medium tyre for their first series of timed laps, with the former having the edge in lap time as Leclerc and Vettel lapped close to half a second quicker.
Valtteri Bottas and Lance Stroll were the latest to overrun Turn 2, where the FIA has installed a slalom of marker boards for drivers to negotiate if they abuse track limits.
Leclerc increased his advantage over Vettel on his first lap in qualifying trim and became the first driver to lap under 1:34s.
A mistake on his first run jeopardised Vettel’s lap and forced him to abandon that attempt, but could only manage to go within seven-tenths of his team-mate.
Verstappen displaced Leclerc at the top of the timesheets with a mighty final sector, the RB15 more than capable to cope with the quick change in direction in the final set of corners.
Hamilton and Bottas could not hook up a decent lap as both lost a vast amount of time in the middle sector to not trouble the top two over one lap, with Bottas the faster of the two Mercedes.
As the session concluded, Verstappen was not to be budged from top spot, leading Leclerc and Bottas with Hamilton and Vettel completing the top five.
Pierre Gasly impressed with sixth fastest ahead of the Racing Point of Sergio Perez. The Frenchman though will too drop five grid positions, while team-mate Daniil Kvyat, who finished outside the top 10, will start his home race at the back of the grid for changing all of his engine elements.
Renault’s Nico Hulkenberg clocked the eighth-fastest lap time in the session, with Lance Stroll and Albon, who spent the majority of FP2 in the garage with mechanical issues, rounding out the top 10 runners.