Daniil Kyvat came out on top of day three of pre-season testing in Barcelona pipping Kimi Raikkonen to top spot with 15 minutes of the day remaining.
Kyvat set the day’s best pace on the C5 compound tyre with a time of 1:17:704s which saw him overtake the Finn for a surprise on day 3.
Williams finally got out on track, with George Russell behind the wheel, after the team had failed to show on the first two days.
Russell was understandably tentative in the opening stages of his laps but eventually got in his grove to complete 23 laps.
Speaking to Sky Sports Russell described the drive as the teams shakedown: “Today was more of a shakedown run - we'll get a proper run-out tomorrow.
“Unfortunately couldn't do that, before we came here but there we go.
"I'm doing my best to help the team, in the long run, I'm trying to help the team,” added the rookie.
Mercedes continued to set slow times with Lewis Hamilton averaging in the 1:22s.
There were three red flags in total, with Romain Grosjean causing two with the second coming just minutes before the end of the session.
Haas have had problems throughout the day with an ignition coil and will be looking to rectify that for the final day.
Carlos Sainz also span out as he tried to break whilst turning on the curb.