File picture: Luca Bruno / AP Photo.

Hockenheim, Germany - Australian Daniel Ricciardo kept Formula One world champion Lewis Hamilton off the top of the German Grand Prix practice timesheets by four thousandths of a second on Friday.

The early pace on a hot morning at Hockenheim will have provided some consolation to the Red Bull driver, who faces a battle through the field in Sunday's race. Ricciardo is set to start from the back of the grid due to engine penalties.

The governing FIA announced on Friday that Red Bull had changed the MGU-K (kinetic motor generator unit), energy store and control electronics on his car. All the changes breach the regulations governing how many elements a driver can use during a season and trigger automatic penalties.

Ricciardo had recognised on Thursday that he faced a big drop but was optimistic he would be able to limit the damage at a circuit with plenty of overtaking possibilities.

Ricciardo's best lap in first practice was one minute 13.525 seconds, versus Hamilton's 1:13.529.

Red Bull's Max Verstappen was third fastest, in 1:13.714, with Ferrari's championship leader Sebastian Vettel fourth in 1:13.796, but on a slower tyre than those above him, in a session without any major incidents.

Finland's Valtteri Bottas, his new Mercedes contract announced an hour before the session started, produced the fifth best time ahead of Ferrari's Kimi Raikkonen.

Renault's Nico Hulkenberg, the only German driver apart from Vettel on the starting grid, tracked wide across the grass but managed to stay clear of the barriers in one of the few moments of note.

Italian test driver Antonio Giovinazzi replaced Sweden's Marcus Ericsson at Sauber for the session, with the car shedding its engine cover on track after leaving the pitlane.

Canadian reserve Nicholas Latifi also had a stint in the Force India that Frenchman Esteban Ocon will race.

Vettel leads Hamilton by eight points ahead of a home race at a circuit not far from his birthplace and where he first fell in love with Formula One as a child in the glory days of Michael Schumacher.