Valtteri Bottas topped the timesheets at the end of the morning session on Day 3 of Formula One pre-season testing at the Circuit de Barcelona-Catalunya in Spain.

An electrical fault caused an early end to Bottas' run on Thursday afternoon in Catalonia, but the Mercedes driver enjoyed a smoother run on Friday and finished fastest with a best lap of one minute, 15.732 seconds.

Renault's Esteban Ocon finished second in the opening segment but was 1.370 seconds slower than the Finn, while Racing Point driver Lance Stroll was third-fastest.

Ferrari's Sebastian Vettel had a morning to forget after he suffered his first red flag of 2020 pre-season testing and recorded just 40 laps, the fewest of any driver on the track during this session. Williams' Nicholas Latifi finished last on the leaderboard after also encountering problems with his FW43.

Red Bull driver Max Verstappen ended up at the other end of that scale with a high of 86 laps on hard tyres, his RB16 coming fifth among the times and just short of two seconds slower than Bottas. 

The official Formula One Twitter account confirmed the fastest times from Friday's morning session:

Friday Morning Recap

It's a testament to Bottas' early performance on Friday that his fastest time was less than half-a-second off the track record he set during qualifying for the 2019 Spanish Grand Prix, per Autosport Live:

Sky Sports F1 highlighted how he raised the bar in testing compared to last year:

Team-mate Lewis Hamilton will rejoin the fray in Friday's afternoon session, but all eyes were on the less celebrated Mercedes star early on in the last day of the first instalment of 2020 testing.

The manufacturer's new "Dual Axis Steering" (DAS) was also back in the spotlight as Bottas sprinted to the best time, but Vettel said he doubts the new, controversial innovation will guide Mercedes to victory in 2020.

The Silver Arrows debuted the new wheel with Hamilton during Thursday's morning testing session, which allows the driver to adjust the car height by pushing and pulling.

Four-time world champion Vettel told reporters in Barcelona: 

"Imagine you are used to do running and you put on your running shoes, and then someone asked you to run in flip-flops. You can also do that, but it just feels very different.

"Obviously it's not quite that extreme, but it's just that you add something that's completely new and feels probably strange and new at first, but obviously if it gives you an advantage, and an edge, then you can fulfil the task and with enough practice, then why not?

"It looks easy to push and pull the steering wheel at certain points of the track, but it's probably not as straightforward."

His Ferrari SF1000 failed to finish Friday's opening portion and encountered trouble after 40 laps:

McLaren's Carlos Sainz recorded a valuable 76 laps in the MCL35 but couldn't muster a lap time faster than one minute, 18.274 seconds.

Hamilton will face a challenge to beat Bottas' time later on Friday, though Mercedes' positive performances thus far in pre-season testing suggest the sky is the limit.