Barcelona - Alfa Romeo driver Kimi Raikkonen produced the fastest lap so far in Formula One's pre-season testing to push his previous team, Ferrari, off the top of the lunchtime leaderboard on Wednesday.
It was the first time since testing started on Monday at the Circuit de Catalunya that Ferrari had not led at the end of a session.
The Finn, returning to the Swiss-based team previously known as Sauber, lapped with a best time of one minute 17.762 seconds on the softest, and fastest, C5 tyre compound.
Ferrari's Sebastian Vettel, his team mate last season, was second fastest in 1:18.350.
Raikkonen's lap was also the first time a team had gone faster in 2019 than they managed in last year's pre-season testing.
Mercedes continued to keep its powder dry, with Finland's Valtteri Bottas the slowest of the nine cars on track but doing more laps than anyone else - 88 to Vettel's 80, both on the same medium C3 tyre.
Renault's Nico Hulkenberg was third fastest in 1:18.800.
McLaren, whose performance has been encouraging over the first two days, missed the first two hours after what it described as "some overnight changes" to the car but managed to get Spaniard Carlos Sainz out for 27 laps before lunch.
Williams continued to be absent from the track but were expected to appear in the afternoon after their much-delayed car reached the track in the early hours after problems finishing building it on time.
British rookie George Russell was scheduled to drive the opening laps for the former champions who finished bottom of the constructors' table in 2018.