Aston Martin's Lance Stroll lapped fastest in Friday's sole free practice session for the Formula One Chinese Grand Prix followed by McLaren's Oscar Piastri, as teams sought to get to grips with a circuit they have not visited in five years.
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How the current ground-effect era cars would respond to the track, and whether an unexpected surface treatment that caught drivers by surprise on Thursday would prove too tough on tyres, was the talk of the paddock leading into the session.
Stroll set the fastest lap of 1 minute, 36.302 seconds at the Shanghai International Circuit, 0.327 quicker than Piastri.
Red Bull's triple world champion Max Verstappen and teammate Sergio Perez were third and fourth.
The weekend will host the first sprint of the season, meaning teams had only one hour to do tyre assessments and evaluate whether simulator data correlated to real track conditions.
The last time F1 raced in Shanghai the cars had 13-inch tyres and generated downforce through aerodynamic appendages on top of the car. They now have 18-inch Pirelli rubber and a design philosophy based around forcing air through tunnels under the car to generate downforce.
While Piastri finished second fastest, earlier in the session the two Mclarens looked to be struggling to turn in, particularly in the first few lower-speed corners.
The teams' ability to finalise their setups ahead of qualifying for Saturday's sprint, which will fix the starting order for the feature race on Sunday, was further tested by a brief stoppage early on due to a small fire next to the track, which led to a red flag.
The Ferrari duo of Charles Leclerc and Carlos Sainz ended 13th and 14th, but were ahead of the two Red Bulls at the top of the timesheets before the teams moved to focus on soft-tyre runs.
Mercedes' Lewis Hamilton, the winner of the last grand prix in Shanghai, was shown a black and white flag after locking up and running off the track and across the pit entry line.
Both Hamilton and teammate George Russell used only hard tyres throughout the session. The pair finished 17th and 18th.
Shanghai-born Zhou Guanyu, China's first and only Formula One driver, was 11th, one spot behind Sauber teammate Valtteri Bottas.
The race has not been held since 2019 due to the Covid-19 pandemic.
The track has seen little use since and could be bumpier than before. Some drivers have voiced concerns over the decision to have a 100km sprint in China when there are so many unknowns.
World champion Verstappen will be hoping to clinch his first-ever win in Shanghai in Sunday's race and extend his lead in the driver's standings.