McLaren's Lando Norris topped the times in Formula One pre-season testing on Wednesday, the first of three days in Bahrain punctured by a power outage that left the pitlane and circuit in darkness.
The lights went out midway through the afternoon session, triggering a one-hour red flag with mechanics scrambling around for flashlights.
Mercedes' George Russell was one of the drivers caught on the hop by the sudden loss of light.
"I came out the pits and thought 'it's suddenly quite dark out here', and I radioed saying I need to change my visor, and I realised there are no floodlights around," said the Briton.
Temperatures were cooler than expected and even rain made an unexpected appearance as F1 rolled up its sleeves and got down to business after last week's glitzy launch for the 75th anniversary season in London.
All eyes in the morning were on one driver as seven-time world champion Lewis Hamilton, resplendent in red, put his new Ferrari team's car through its paces in the morning stint.
The 40-year-old completed 70 laps, finishing four tenths of a second slower than Kimi Antonelli, the teenager who replaced him at Mercedes.
"To be here with Ferrari is an incredible feeling," said Hamilton, who ended the day with the 13th best time.
"Our aim is to test as much as possible, get a maximum amount of data and to familiarise ourselves with the car.
"I've already learned a lot. It's too early to speak about performance, but I'm already feeling comfortable."
Antonelli, 18, put in an assured performance as he prepares for his rookie season with the Silver Arrows, the Italian clocking a morning fastest time of 1min 31.428sec.
Liam Lawson, making his official debut as a fully fledged member of the grid for Red Bull, finished closest before the lunch break at 0.132 behind the Mercedes.
Lawson's new teammate, four-time reigning world champion Max Verstappen, took over for the afternoon session.
- 'Super competitive' -
The Dutchman banked over 65 laps to finish the day with the third quickest overall time behind Norris, who finished second in the 2024 drivers' championship, with Russell splitting the pair.
Norris posted the day's fastest lap of 1min 30.430sec, with Russell at 0.157sec and Verstappen at 0.244.
Charles Leclerc for Ferrari came fourth, ahead of his former teammate Carlos Sainz, now with Williams.
Timings in testing are notoriously difficult to decipher, with unknown fuel loads and teams working on different strategies.
But even so on the evidence of day one's testing the 75th anniversary season could be one to remember with less than one second covering the top seven drivers.
"I can see it being super competitive," said McLaren CEO Zak Brown.
"Last year four teams won multiple races, this year I could see that being even more. I'm more excited than nervous" he added.
All 10 teams are in Bahrain to fine tune their 2025 cars ahead of the opening race in Australia on March 16.
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