Barcelona, Spain - Formula One world champion Mercedes predicted a three-way title battle as the second pre-season test started on Tuesday with Ferrari and Red Bull showing their pace.
Ferrari's Sebastian Vettel was fastest, lapping in 1m20.396s and completing 171 laps - equal to nearly 800km and more than two and a half race distances at the Circuit de Catalunya. Vettel posted his fastest lap on the medium tyres, with Mercedes' Valtteri Bottas second on softs with a time 0.200s slower.
Dutch 20-year-old Max Verstappen was third on the timesheets for Red Bull in 1m20.649, completing 130 laps.
Mercedes team boss Toto Wolff said later: "What we have seen is that even if it is best case we are not in front by a lot, and if it is a worst case we are not far behind.
"What we have seen from Red Bull is that they have a very strong package," added the Austrian, whose Mercedes team is going for its fifth consecutive Drivers' and Constructors' championship double. "I think it will be all three of us against each other."
Bottas and four times world champion team-mate Lewis Hamilton shared testing duties, with Bottas putting in 86 laps and Hamilton Briton 91 - a total of 824km between the pair.
"We have not worked too much on fine-tuning the set-up as we're mostly still gathering information," commented Hamilton. "In the next couple of days, once we get into the long-runs and some shorter qualifying-style runs, we will get a better idea of where the car is."
After snow and rain hit last week's first test, dry conditions and bright skies greeted teams with some gusts of wind later on.
"It was a good day’s work," said Vettel. "We managed to get through our programme, even if the conditions weren’t always ideal because of the wind."
McLaren endured another difficult day, with Stoffel Vandoorne's Renault-powered car suffering electrical and hydraulic failures and doing the fewest laps.
McLaren's racing director Eric Boullier commented: "Today wasn’t the day we had hoped for on track, but, despite this, we aren’t overly concerned about the issues we faced.
"It’s obviously not the productive day we had planned, but the problems are the types of niggles that we almost hope and expect to face during testing, in order to prepare us properly for the season ahead.".
Toro Rosso, now working with Honda after the Japanese manufacturer's parting from McLaren, was fifth on the timesheets while Vandoorne was 12th.
The first race will be in Australia on 25 March.