The Azerbaijan Grand Prix is live on 5 Live and the BBC Sport websiteRed Bull's Sergio Perez continued his strong form with fastest time in first practice at the Azerbaijan Grand Prix.
Perez, who won the last race in Monaco, was 0.127 seconds faster than Ferrari's Charles Leclerc, with the second Red Bull of Max Verstappen third.
Verstappen leads Leclerc by nine points in the drivers' championship and Mexican Perez a further six adrift.
Ferrari's Carlos Sainz was fourth, ahead of Alpine's Fernando Alonso and Lewis Hamilton's Mercedes.
The Red Bull and Ferrari were closely matched as ever but the way they were generating their lap time did not appear to augur that well for the Italian team.
The Ferraris were losing several tenths of a second in the final sector, which primarily comprises the long final 'straight'.
If that trend continued into Sunday, Ferrari would be extremely vulnerable to being passed by the Red Bulls even if they qualify in front.
Leclerc is in need of a strong result this weekend after Ferrari bungled his strategy in Monaco, dropping him from what should have been a victory to fourth place.
It was the latest in a series of mishaps which have seen Verstappen turn what had been a 46-point deficit after the first three races into a nine-point advantage.
Behind Hamilton, Alpha Tauri's Yuki Tsunoda was seventh quickest, from Mercedes driver George Russell, the second Alpha Tauri of Pierre Gasly and Alpine's Esteban Ocon.
Verstappen ended the session with a spin at Turn 15, in which he somehow managed to rotate the car without hitting the wall on the outside.
Verstappen complained that the car was suffering from understeer when he was off throttle coming into that corner.
It was a difficult session for Williams' Nicholas Latifi and Haas' Mick Schumacher, both of whom suffered car failures early in the session and lost what could be valuable mileage.
