BARCELONA, Feb 27 (Reuters) - World champions Mercedes pounded out the laps while Ferrari went fastest and rivals Red Bull and McLaren hit immediate setbacks as Formula One's new crop of cars made their test debuts on Monday.
Valtteri Bottas, replacing retired world champion Nico Rosberg at Mercedes alongside Lewis Hamilton, had completed well over a race distance by lunchtime with 79 timed laps of the Circuit de Catalunya.
Ferrari's Sebastian Vettel, a four times champion with Red Bull but without a win last year, was fastest in the sunny opening session with a lap of 1:22.791 seconds and 62 laps to his credit on medium tyres.
The German's time was already close to the fastest lap in 2016 Barcelona testing of 1:22.765.
Bottas was second on the timesheets, 0.378 slower on the soft tyres.
The main focus of all teams was on reliability and racking up mileage, however, with some cars sporting intricate aerodynamic devices to measure air flow and performance.
Fernando Alonso failed to set a timed lap on home soil in the McLaren while Australian Daniel Ricciardo, first to drive the new Red Bull RB13 after its presentation on Sunday, had completed only four.
McLaren's engine partners Honda said the orange and black MCL32 car, which managed just one untimed installation lap, had an oil systems problem.
"We plan to run again today but due to the difficult access location it will take several hours to resolve," a spokeswoman said.
Ricciardo brought out the first red flag of the morning, stopping on track with a sensor problem between turns three and four. The car was brought back to the pits shrouded in a tarpaulin on the back of a flatbed truck.
It was craned off and taken back into the garage, where mechanics were working on removing the gearbox.
Force India's Mexican driver Sergio Perez and Williams driver Felipe Massa were third and fourth fastest and completed 39 laps each.
Of the rest, only Sweden's Marcus Ericsson came close to their lap tally with 32 for Sauber, who are using last year's Ferrari engine. Renault's Nico Hulkenberg had the honour of being first on track.
The new cars, wider and with bigger front and rear tyres, are expected to be several seconds a lap quicker than last year's, if no louder.
The season starts in Australia on March 26. (Reporting by Alan Baldwin; Editing by Alison Williams)