New Mercedes driver Valtteri Bottas broke the all-time lap record at the Circuit de Barcelona-Catalunya on Wednesday during morning testing.
The flying Finn used super-soft tires to clock a time of one minute 19.705 seconds, the fastest ever recorded at the track since it was redesigned in 2007.
"Not only has Valtteri Bottas clocked the most laps of anyone _ 75 _ he's also shown ominous pace, with his ultra-soft run unofficially the fastest lap ever seen on this layout of the Barcelona circuit," the organizers said in a statement.
The reigning world champion, retired driver Nico Rosberg, was on hand at the track and approached the pit lane to see his old team and all the new race cars up close.
Rosberg talked to Bottas and came away impressed with how the revised regulations have altered the cars for the new season and looked set to take the drivers to new physical limits.
"The cars are going to take them to the limit, physically also _ even now they're hurting bad, all of them," Rosberg told fans.
"Definitely looking good on that front because they look like proper monsters, I mean, wow," Rosberg added.
"That's how it should be you _ F1 should be very, very extreme," the champion said.
Rosberg said he liked the "beastly" sound of the engines this year and felt the drivers this season would "end up exhausted after the races," he added.
"Mercedes is going to be fast," he said.
Fernando Alonso aboard his McLaren had a more profitable morning than he did two days ago when he could not test at all during the morning session.
Still, the mechanics proved busier than the driver as he was only able to complete 28 laps, in which his best time was just over four seconds slower than Bottas.
Once again, it was Mercedes that set the pace, something that could be disquieting for its rivals given that after three consecutive years of an almost insulting dominance in the sport it was expected that Ferrari or Red Bull could draw closer.
After two-and-a-half days testing, the times on the track suggest that little or nothing had changed.
The Finnish driver clocked a spectacular lap almost three hours after the track was opened, with blistering 1:19.838, a time that broke the track record.
However, it did not take long to break it once again, with a 1:19.705 that came after 71 laps.
Since the track layout changed in 2007, the fastest lap had been clocked in at 1:19.995s, a time set in 2010 by Red Bull's Mark Webber.
The first incident on the track came when British driver Jolyon Palmer (Renault) left the track and caused a red flag.
Later, Lance Stroll spun his Williams in the final stretch of the session.
Alonso spent many laps setting up his car and then stopped the clock at 1:23.832, eventually completing 28 laps.
Australian Daniel Ricciardo (Red Bull) was the second-fastest driver in the morning session, 1:448 slower than Bottas, with Palmer 1.691 slower than the Finn.
Sebastian Vettel was unable to improve the previous day's time aboard his Ferrari.
His teammate Kimi Raikkonen had been able to set a time of 1:20.960 during his 108 laps of testing.
Wednesday, Vettel was unable to go below 1:21.609.
The Russian Daniil Kvyat was in charge of taking the Toro Rosso out on track in the morning, with afternoon testing passing over to the Spanish Carlos Sainz Jr.
The Mexican Alfonso Celis completed 39 laps with Force India, but with his best time of 1:23.781 he was far from the best time set by French teammate Esteban Ocon 1:22.509.
1.- Valtteri Bottas, FIN-Mercedes, 1:19.705, 75 laps
2.- Daniel Ricciardo, AUS-Red Bull, 1:21.153, 48 laps
3.- Jolyon Palmer, GBR-Renault, 1:21.396, 51 laps
4.- Sebastian Vettel, GER-Ferrari, 1:21.609, 69 laps
5.- Marcus Ericsson, SWE-Sauber, 1:21.824, 54 laps
6.- Lance Stroll, CAN-Williams, 1:22.351, 56 laps
7.- Alfonso Celis, MEX-Force India, 1:23.781, 39 laps
8.- Fernando Alonso, SP-McLaren, 1:23.832. 28 laps
9.- Daniil Kvyat, RUS-Toro Rosso, 1:23.952, 31 laps
10.- Romain Grosjean, FRA-Haas, 1:25.133, 27 laps.