Max Verstappen knocked Ferrari rival Charles Leclerc off the top of the timesheets to go fastest on the opening day of practice for the Russian Formula One Grand Prix. The Red Bull driver was narrowly edged out by Leclerc, winner of two of the last three races, in Friday's opening 90 minutes of running. But the Dutchman, also a two-time winner this year, struck back with a one minute 33.162-second lap after lunch, ending the day 0.335 seconds quicker than the Monegasque. "Today was very positive and the car worked really well on both tyres," said Verstappen, who is carrying a five-place engine-related grid penalty. Valtteri Bottas was third ahead of championship leader Lewis Hamilton. The Mercedes team mates moved ahead of Ferrari's Sebastian Vettel, whose win in Singapore last week ended a 13-month drought for the four-time champion, with the German slipping from third to fifth. But it was an uncharacteristically off-colour day for the usually dominant champions, with the silver cars hindered by niggling problems in the morning and a lack of pace that saw them end the day more than half a second off Verstappen's best. "It's been a day of discovery and exploring," said Hamilton, who complained of braking problems in the opening session and is hoping for a wet qualifying session on Saturday. "We've just been trying to figure out how we can improve the car but it's not an easy task," the five-time champion added. Despite their lack of form which some commentators suspected was down to sandbagging — when teams deliberately run slower to hide their car's true potential — Hamilton and Mercedes remain on course for a record sixth title double. The Briton, winner of eight races this year, leads Bottas by 65 points in the overall standings and is 96 clear of Verstappen and Leclerc, his closest non-Mercedes challengers who are joint third, with six races to go. The German team, winners of 10 of this season's 15 races, lead Ferrari by 133 points in the constructors' standings. But they head into Sunday's Russian round, a race they have won every year since it joined the calendar in 2014, reeling from three successive defeats at the hands of rivals Ferrari. A fourth loss this weekend, unprecedented for the German outfit in Formula One's turbo-hybrid era, will set alarm bells ringing at their Brackley headquarters. For Ferrari it will offer evidence that their resurgence, albeit late, is real. "There is still quite a lot of lap time to be gained on our side," said Leclerc, who has started the last three races from pole and was left fuming after Ferrari's strategy denied him a third consecutive win in Singapore last week. "The balance was not exactly how I wanted it to be, especially in the qualifying runs. But the race pace looked very strong," the 21-year-old added. Home hero Daniil Kvyat, the only Russian on the grid, endured a difficult start to his weekend. Already set to start Sunday's race from the back of the grid in his Honda-powered Toro Rosso, the 25-year-old ground to a halt in the morning with a suspected fuel system issue. He was then involved in a near miss with team mate Pierre Gasly on his way to the 12th-fastest time in the second session. Daniel Ricciardo spun his Renault backwards into the barriers in the closing stages of the first 90-minute session and crawled back to the pits with a dislodged rear wing. There were two brief virtual safety car periods during the day.