Lewis Hamilton of Mercedes set the fastest lap on the first day of Formula One's 2017 pre-season testing, which commenced at the Circuit de Barcelona-Catalunya in Barcelona on Monday.
The Brit completed 73 laps in Spain, setting the quickest time of 1 minute, 21.765 seconds to top the timesheet.
New team-mate Valtteri Bottas took Mercedes' W08 for its debut test in the morning, but could only post the sixth-fastest time as he pushed the latest vehicle from the constructor.
Here's a look at the fastest laps on the opening day, according to Formula One's official Twitter feed:
Hamilton once again proved he will be the man everyone wants to beat on the track this season as he edged out Sebastian Vettel for the fastest lap time in the first day of testing.
The German had been quickest in the morning as he sprinted around the track until Hamilton climbed into his car in the afternoon.
Formula One provided the classification after the morning's session:
Vettel and Bottas played out an exciting duel during the early session as they traded the fastest lap back and forth throughout proceedings, with the former world champion ultimately coming out on top.
Both constructors will have been pleased with the reliability their new cars showed, with the pair completing almost 150 laps combined before the afternoon.
Red Bull and McLaren had less reason to be pleased, though, as they debuted their RB13 and MCL32 cars.
Driving the former, Daniel Ricciardo saw the red flags emerge for the first time this season when his car came to a halt just four laps in.
F1 and Red Bull's official Twitter feeds provided more details:
Fernando Alonso and McLaren had a similarly frustrating time, as a problem with the car's oil system restricted the Spaniard to just one lap in the morning.
Kevin Magnussen of Haas also faced some issues after completing seven laps. He was eventually able to get back out on the circuit, only for his morning to end badly:
Hamilton was the star of the afternoon as he attacked the corners in his new car, but Ferrari showed they have a vehicle that should compete for the championship this season.
Vettel was just 0.113 second behind his rival, with the added bonus of completing a mammoth 128 test laps.
Bottas has much to live up to after replacing reigning champion Nico Rosberg but was pleased with his first outing for the Silver Arrows.
According to Andrew Benson of BBC Sport, the driver said:
It's very nice to start proper testing and it was a good morning, lot of laps, no issues and some good tests.
F1 has introduced new rules this season aimed at making the cars up to five seconds a lap faster and more demanding for the drivers.
It is a bigger car. It has more downforce and you can feel it is heavier. The corner speeds are quite a bit higher.
It is more demanding but luckily I am well prepared for the season. I like the stability especially in the high-speed corners. There is a lot of grip in the car. I very much enjoyed it.
Mercedes were formidable on the first day of testing, but Ferrari showed very good pace and reliability.
However, it was a mixed set of results for the other teams, and they will need to quickly fine tune their cars to increase their performances.