F1 champion Max Verstappen of Red Bull Racing edged out Charles Leclerc of Ferrari to the fastest time in Friday's practice for the season-opening Bahrain Grand Prix as both teams lived up to their pre-season hype while Mercedes appeared to be on the back foot.

The 24-year-old lapped the 5.4km floodlit Sakhir track in one minute 31.936 seconds, beating Leclerc by 0.087 seconds. Ferrari's Carlos Sainz was over half a second back in third.

"It's been a positive day for us, really," said Red Bull team boss Christian Horner.

"Both in the warmer conditions earlier in the day and that last session, the short run and the long run both looked pretty decent ... we're pretty satisfied with today's running."

Mercedes, gunning for a ninth consecutive constructors' crown, have struggled to dial their car into the Sakhir circuit's layout and appeared to be lagging behind.

New recruit George Russell was just over half a second off Verstappen's pace in fourth, while teammate Lewis Hamilton was 1.2 seconds slower than the Dutchman's time in ninth.

"As you can see, we're a long way off," said Hamilton, again adding that he did not expect Mercedes to be in the fight for victory on Sunday.

"We're not bluffing like before like people assume we are. We'll work as hard as we can through it and do what we can."

Aston Martin's Nico Hulkenberg, standing in for Sebastian Vettel, who has tested positive for COVID-19, ended 17th, only a tenth off his teammate Lance Stroll in 16th.

Haas's F1 returnee Kevin Magnussen, replacing sacked Russian Nikita Mazepin, ended the day 10th behind Hamilton. His teammate Mick Schumacher was eighth, marking an encouraging start to the season for the outfit.

Daniel Ricciardo, back in his McLaren after having recovered from COVID-19, completed just 12 laps in the second session to end the day 18th. His teammate Lando Norris was 11th.

Chinese racer Zhou Guanyu is the only rookie on the grid with Alfa Romeo. He finished 15th behind AlphaTauri's Pierre Gasly and Yuki Tsunoda.

(With input from Reuters)