Sebastian Vettel finished the opening day of 2016 pre-season Formula 1 testing fastest for Ferrari, but it was reigning champions Lewis Hamilton and Mercedes who racked up the laps.
Vettel's leading time of 1m24.939s at Barcelona's Catalunya circuit was posted late in the morning session on a set of medium-compound Pirelli tyres.
He only managed 69 laps overall - 36 in the morning, 33 in the afternoon - compared to Hamilton's phenomenal total of 156. The Mercedes driver's best was just under half a second off Vettel.
To put Hamilton's lap-count total into perspective, no other driver came close to even 100 laps, with the next best being Marcus Ericsson's 88 for Sauber.
Red Bull's Daniel Ricciardo finished best of the rest, just over a second off the pace in an RB12 that still sports a Renault engine, albeit badged TAG Heuer in the wake of last season's acrimonious fallout between team and manufacturer.
Valtteri Bottas was fourth on the timesheet, just 0.047s behind Ricciardo, with Force India reserve Alfonso Celis Jr a solid fifth on his F1 debut.
Celis's best time of 1m26.298s was set on the soft compound, with the Mexican finishing four tenths of a second up on Jenson Button in his McLaren, the Briton also running the slightly quicker rubber for his best lap.
Button also clocked up 84 laps, five more than McLaren-Honda posted over all four days of last season's first test at Jerez ahead of what eventually proved to be a torrid year for the Japanese manufacturer on its return to F1.
Running in an unmarked Toro Rosso as the livery is still in the pipeline and to be unveiled from the start of the second test next Tuesday, Carlos Sainz Jr was seventh, 2.2s adrift of Vettel.
In last year's Sauber as the 2016 model will not be ready until test two, Marcus Ericsson was eighth quickest, with the Swede 2.6s off the pace.
Pascal Wehrlein produced an encouraging display on his Manor debut with a time 3.3s behind Vettel.
After managing just eight laps in the morning as Manor only received a number of parts late last night, the 2015 DTM champion managed 46 in the afternoon.
A front-wing failure in the morning session compromised Haas's maiden outing, with Romain Grosjean winding up 10th on the timesheet, and managing just 31 laps for the day, with his best a 1m28.399s.
Bringing up the rear on a day full of "niggles", according to Jolyon Palmer, was Renault. The Briton was just over four seconds down and with only 37 laps to his name.
MONDAY TEST RESULTS:
|3||Daniel Ricciardo||Red Bull/Renault||1m26.044s||1.105s||87|
|5||Alfonso Celis||Force India/Mercedes||1m26.298s||1.359s||58|
|7||Carlos Sainz||Toro Rosso/Ferrari||1m27.180s||2.241s||55|