Sebastian Vettel set the fastest lap ever recorded around the Circuit de Catalunya on the penultimate day of pre-season testing.
The German was more than a second quicker than anyone else as Ferrari finally showed their hand before the start of the season later this month.
Kevin Magnussen's Haas was an eye-opening second fastest ahead of Pierre Gasly's equally surprising Toro Rosso.
Lewis Hamilton was only eighth fastest for pre-season favourites Mercedes.
- BBC Radio 5 live's 2018 season preview
- Relive the third day of the final pre-season test
- Make your winners & sinners predictions
The world champion was more than two seconds slower than 2017 title rival Vettel as his team focused on longer runs and heavy fuel loads.
"I am pretty happy with the laps I had and the feeling I got for the car. But it is the wrong time to draw any conclusions (about pace)," Vettel said.
Pre-season testing times are notoriously unreliable guides to actual form because the specification in which the cars are running is not known. Fuel loads, engine modes and tyre compounds all make a significant difference to performance.
After a difficult run of reliability problems in pre-season testing so far, it was a better day for McLaren. The team did more than 100 laps in a day for the first time all winter and Stoffel Vandoorne was sixth fastest overall.
- I hope to see a female F1 world champion - Toto Wolff
There is still no clear picture of competitiveness going into the first race in Australia on 23-25 March.
But the indications are that Mercedes, who have won the last four world titles, have an advantage over the field, with Ferrari and Red Bull their closest challengers.
Fastest times on the third day of the final pre-season test
1 Sebastian Vettel (Ger) Ferrari 1:17.182 ****
2 Kevin Magnussen (Den) Haas-Ferrari 1:18.360 **
3 Pierre Gasly (Fra) Toro Rosso-Honda 1:18.363 ****
4 Nico Hulkenberg (Ger) Renault 1:18.675 ****
5 Carlos Sainz (Spa) Renault 1:18.725 ****
6 Stoffel Vandoorne (Bel) McLaren-Renault 1:18.855 ****
7 Marcus Ericsson (Swe) Sauber-Ferrari 1:19.244 ****
8 Lewis Hamilton (GB) Mercedes 1:19.296 **
9 Valtteri Bottas (Fin) Mercedes 1:19.532
10 Robert Kubica (Pol) Williams-Mercedes 1:19.629 **
11 Sergio Perez (Mex) Force India-Mercedes 1:19.634 ****
12 Max Verstappen (Ned) Red Bull-Renault 1:19.842 *
13 Lance Stroll (Can) Williams-Mercedes 1:20.276 *
**** = time set on hyper-soft tyre; ** = super-soft tyre; * = soft; all others medium