Lando Norris topped the timesheet for McLaren, but it was the performance of Max Verstappen's Red Bull that impressed the paddock on the first day of Formula 1's pre-season test in Bahrain.
The three-day test at the Bahrain International Circuit is the second of three events that form an extended pre-season testing schedule designed to give Formula 1's teams the opportunity to adapt to the introduction of new power unit and chassis regulations for the 2026 season.
Red Bull, who are manufacturing their own engine for the first time since entering the sport in 2005, had already gone some way to dispelling doubts over the power unit with a strong showing at last month's Barcelona shakedown, but they made another statement on Wednesday in Bahrain.
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Verstappen was first on track and topped the timesheet for much of the day, but more crucially was able to amass an impressive total of 136 laps and put together some eye-catching longer stints during the second of the day's two four-hour sessions.
He was ultimately dislodged from top spot by reigning world champion Norris with just over an hour to go, and the Brit's time of 1:34.669s ensured he finished the day 0.129s clear of Verstappen in second.
At this relatively early stage of testing, with the rest of this event plus a further three days to follow in Bahrain next week before the season-opening Australian Grand Prix on March 8, the best individual lap times must be viewed with caution due to the fact teams aren't necessarily chasing maximum performance at this stage.
There's also the fact that teams might want to disguise their true pace up until qualifying in Melbourne, which some onlookers thought might have been the case with Mercedes on Wednesday as their best effort came from George Russell, who was 1.5s off the pace in sixth.
Mercedes also endured a disrupted afternoon as Kimi Antonelli was kept in the garage for more than half of the second session, before amassing 30 laps in the final hour and moving up to 11th on the timesheet.
Charles Leclerc was half a second back from Norris in third for Ferrari, which was able to amass a solid lap count but once more appeared particularly difficult to handle, with Lewis Hamilton's spin in the morning session highlighting the challenge.
There were two red flags during the day, the first caused by Alpine's Franco Colapinto stopping out on track, but the issue didn't keep the Argentine off track for long.
Audi's Nico Hulkenberg brought out a second red flag in the afternoon session, but was able to get his car restarted on track, allowing the action to resume almost immediately.
Having missed the entire Barcelona test after failing to have their car ready, Williams had a strong first day as Carlos Sainz and Alex Albon combined for 145 laps - the highest total for any team on Wednesday.
Aston Martin, who only made it on track for the final stages of the Barcelona event, were less impressive as Lance Stroll was limited to just 36 laps by a power unit issue and finished more than five seconds off the pace.
F1's brand new team for 2026, Cadillac, continued their steady progress as Valtteri Bottas and Sergio Perez combined for 107 laps.
Wolff: Red Bull are the benchmark
Mercedes boss Toto Wolff said Red Bull were setting "the benchmark" in Bahrain, while McLaren chief Zak Brown and Williams team principal admitted they were also impressed by the Milton Keynes squad.
Wolff said: "I was hoping they would be worse than they are. They have done a very good job.
"The car, the power unit, are the benchmark at the moment I would say. Then obviously you have Max in the car, the combination is strong.
"Look at their energy deployment today. They are able to deploy far more energy on the straights than everybody else. We are speaking a second per lap, over consecutive laps.
"On a single lap, we've seen it before, but now we have seen it on 10 consecutive laps with the same kind of straight line deployment.
"I would say that as per today, on the first official day of testing, which is always the caveat of that, they've set the benchmark today."
Vowles revealed Williams are seeing data which suggests Red Bull gain over half a second on the home straight alone at the Bahrain International Circuit.
He told Sky Sports News: "We are seeing six tenths consistently. Into Turn 1, we can't get close to that. There speed into Turn 1 is mightily impressive.
"The Red Bull from scratch to be built on an entirely new programme, to deliver it, be reliable and deliver performance with it. They have achieved all of that."
Brown, speaking before McLaren's Norris had replaced Verstappen at the top of the timesheet, told Sky Sports F1: "I think we can't come to any firm conclusions. If I had to go Vegas (to bet on it), it looks like the big four are the big four, kind of hard to tell in what order.
"Mercedes were very strong in Spain. Max has done some great lap times around here. But it kind of looks like the grid is in a similar position."
Off the track, the main talking point continued to be Mercedes' engine, which the sport's four other power unit manufacturers are understood to be questioning the legality of amid a dispute of the interpretation of compression ratio limits.
Wolff maintained that his team's engine is "100 per cent legal", but his former driver Hamilton was among those to take an opposing stance, urging the FIA to ensure "we're all starting on an equal playing field".
Sky Sports F1's Bahrain Testing schedule
Test One: Thursday 12th, Friday 13th February
- 3pm: Final hour of track running Live
- 8pm: Testing Wrap
- 8.30pm: Ted's Testing Notebook
Test Two: Wednesday 18th, Thursday 19th, Friday 20th February
- 6.50am-11.05am: Morning session Live
- 11.55am-4.10pm: Afternoon session Live
- 8pm: Testing Wrap
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(c) Sky Sports 2026: F1 Bahrain testing: Lando Norris tops timesheet on first day but Max Verstappen's Red Bull impresses rivals
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