Barcelona – Kimi Raikkonen put Ferrari on top of the timesheets after the second day of Formula One's pre-season testing on Tuesday but Mercedes still led the way on kilometres covered.
Raikkonen was a mere 0.023 faster than triple champion Lewis Hamilton at the end of the day, although the Briton got out at lunchtime and handed his Mercedes to new team-mate Valtteri Bottas.
Ferrari's Finn had been second quickest in the morning, but on slower medium tyres than Hamilton's supersofts. He set his fastest time on softs in the afternoon.
While Raikkonen ended the day with 108 laps under his belt, the Mercedes pair put in 168 laps between them after an untroubled 152 on Monday.
Hamilton's 66 were the equivalent of a Spanish Grand Prix race distance.
Reliability more than the lap times is the main focus at this stage of the year with the new-look wider cars, on fatter front and rear tyres and with revamped aerodynamics, unveiled only last week.
Ferrari, which has kept its cards close to its chest with no media activities on the first two days after a low-key online launch, also showed good reliability on Monday with Sebastian Vettel completing 128 laps.
Raikkonen's best lap of one minute 20.960 seconds compared to the fastest time in 2016 Barcelona testing of 1:22.765.
Red Bull and McLaren, who had a troubled debut day, had mixed fortunes on day two.
Dutch teenager Max Verstappen did 89 laps for Red Bull but Belgian rookie Stoffel Vandoorne managed only 40 in the McLaren and was second slowest. Vandoorne was halted after 29, and partners Honda changed the power unit.
"I think it was positive to get back behind the wheel after four months of no driving," said former GP2 champion Vandoorne, looking on the bright side.
"It was a good first feeling for me and I immediately felt confident in the car and very comfortable... unfortunately we had a loss of engine power during the morning after a couple of laps, we're still investigating what the issues are."
Others also wrestled with garage gremlins.
Renault's Jolyon Palmer managed to do one untimed installation lap in the morning, after the team flew in new parts overnight, but ended the day with 53 done.
Italian Antonio Giovinazzi, standing in for the injured Pascal Wehrlein at Sauber, did five before the team swapped out the Ferrari power unit and then 62 more after lunch.
Canadian teenage rookie Lance Stroll spun off after 12 laps, going through the gravel backwards and damaging his Williams, forcing the team to abandon testing for the day.