BARCELONA (Reuters) - Formula One world champions 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 one minute 20.396 seconds and completing 171 laps -- equal to nearly 800km and more than 2-1/2 race distances at the Circuit de Catalunya.
The German did his fastest lap on the medium tyres, with Mercedes' Valtteri Bottas second on softs with a time 0.200 slower.
Dutch 20-year-old Max Verstappen was third on the timesheets for Red Bull in 1:20.649, doing 130 laps.
"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," Mercedes team boss Toto Wolff told Sky Sports television.
"What we have seen from Red Bull is that they have a very strong package," added the Austrian, whose Mercedes team are going for their fifth drivers' and constructors' championship double in a row.
"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 the Finn putting in 86 laps and the 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 program, 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.
Toro Rosso, now working with Honda after the Japanese manufacturer's parting from McLaren, were fifth on the timesheets while Vandoorne was 12th.
"Today wasn’t the day we had hoped for on track, but, despite this, we aren’t overly concerned about the issues that we’ve faced today," said McLaren's racing director Eric Boullier.
"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."
The first race is in Australia on March 25.
(Reporting by Alan Baldwin in London, editing by Ken Ferris)