MONTMELO, Spain (AP) Ferrari driver Sebastian Vettel recorded the fastest preseason lap during the second-to-last day of Formula One testing on Thursday.
Vettel pushed his Ferrari to 1 minute, 19.024 seconds, bettering his mark from earlier in the day, which was faster than that clocked by Mercedes driver Valtteri Bottas on Wednesday.
Vettel, however, said he has learned from Mercedes' three-year dominance of the series that the defending champions are likely holding something back.
''If you look at how many laps Mercedes have done, look at historically how slow they go in testing, how much they were able to ramp it up for the races, it's clear. They are very fast with their long run pace. They're the ones to beat,'' Vettel said.
''For us it doesn't really matter where we are now. We are growing and we need to work hard. That's why it's important not to get distracted.''
Vettel also led the pack with 156 laps completed on a full eight hours of driving.
Bottas' previous leading mark was already the fastest ever recorded at the Circuit Barcelona-Catalunya since layout changes made a decade ago. After a chicane was introduced in 2007, the best lap time was set by former Red Bull driver Mark Webber during 2010 qualifying.
Times continued to drop through day seven of the preseason as expected after F1 issued a major rulebook overhaul this winter to make wider, and thus faster, cars.
Mercedes driver Lewis Hamilton was second best to Vettel in the four-hour morning session, only 0.326 seconds off Vettel's pace. Bottas took over for Mercedes in the afternoon and had the eighth quickest time.
Bottas said Mercedes was also expecting more from its rivals, especially Ferrari, come the season-opening Australian Grand Prix.
''We aren't confident we are in the front. We are not relaxing,'' Bottas said. ''We do feel the other teams are progressing.''
While Ferrari and Mercedes sized each other up, McLaren suffered another demoralizing setback after Stoffel Vandoorne's car twice puttered to a halt on the track. The team said the second stoppage was due to an electrical problem. McLaren has been plagued by stoppages and slow speeds from its Honda motor.
Esteban Ocon enjoyed a promising day with the third fastest time and next highest workload with 137 laps in his Force India.
Daniel Ricciardo, meanwhile, could manage only the sixth best lap in his Red Bull over 128 laps.
Williams, which impressed with its speed in Spain, was down at the bottom of the time sheet. Lance Stroll and Felipe Massa were the two slowest in the field, more than five seconds behind Vettel.
Friday will be the last chance for teams to make their preparations for the Australian GP on March 26.