The Chinese racer's lap time was faster than what was managed during testing at the same venue last year, despite tweaks to the technical rules, although it was set on the very softest Pirelli tyre compound so is not truly representative.
However, the Red Bull - in the hands of Max Verstappen, at least - is looking genuinely quick, while Fernando Alonso continued to impress for Aston Martin.
But there were some reliability gremlins, most notably for Mercedes, which suffered a less than ideal day.
PLUS: What we learned on day two of F1 testing in Bahrain
Martyn Lee is joined by Matt Kew from the Bahrain media centre to discuss the key talking points from the day's testing.
Source: Autosport