Sebastian Vettel continued Ferrari's strong opening day of Formula 1 testing in Barcelona, finishing on top of the times.

Vettel had set a 1m18.161s in the morning session on the 'C3' tyres, 1.783 seconds quicker than his nearest rival Sergio Perez in the Racing Point car.

While he didn't improve his laptime in the afternoon, Vettel increased his lap count to 169 by the end of the day, which was enough to head the mileage rankings as well, although his margin over the field was reduced.

Romain Grosjean decreased Vettel's advantage at the top to under a second, with a late lap on the C3 tyre within the last half-hour snatching second spot from Carlos Sainz.

However, McLaren driver Sainz stole it back with a 1m18.558s to trail Vettel by just 0.397s.

Sainz had helped to bring out the first red flag of the afternoon when he stopped at the exit of the pitlane at the beginning of the running. He blamed a loss of power for the issue, and the car appeared to run smoothly thereafter.

Grosjean had to settle for the third-fastest time, but Haas had a much better afternoon. Grosjean's car had ground to a halt entering the final chicane with fuel pressure issues earlier in the day.

Red Bull-Honda's Max Verstappen managed to net 128 laps and set the fourth-fastest time behind Vettel, Sainz and Grosjean.

Kimi Raikkonen kept Alfa Romeo in the top five, after setting the fourth fastest time earlier on in the day. He ran C2 and C3 tyres and had been as high as second on the timing screens, but was shuffled back later in the afternoon.

Alfa Romeo was still one of the teams to log more than 100 laps, despite Raikkonen's visit to the gravel bringing out the first red flag of the morning session. His car stopped again with just over a minute left in the afternoon session, causing another red flag.

The Toro Rosso of Daniil Kvyat and Perez took the sixth and seventh fastest times respectively, but both teams would likely have wanted more running.

Kvyat needed to bolt the C4 tyre on to set his best time, while Perez only added 10 laps to the 20 he completed in the morning, with his team finishing bottom of the laps-completed order.

After taking over the Mercedes in the afternoon, reigning champion Lewis Hamilton didn't beat Valtteri Bottas's eighth place in the order by the end of the day, but he did complete more laps with 81.

Behind the pair of Mercedes, Renault had a disappointing day in terms of times as its drivers rounded out the order.

New Renault driver Daniel Ricciardo took over from Nico Hulkenberg for the afternoon, but missed out on beating Hulkenberg by 0.003s. He also completed 21 fewer laps than the German driver.

Testing times, Day 1:

Pos | Driver | Team | Time | Gap | Laps
1 | Sebastian Vettel | Ferrari | 1m18.161s | 169
2 | Carlos Sainz | McLaren | 1m18.558s | +0.397 | 119
3 | Romain Grosjean | Haas | 1m19.159s | +0.998 | 65
4 | Max Verstappen | Red Bull | 1m19.426s | +1.265 | 124
5 | Kimi Raikkonen | Alfa Romeo | 1m19.462s | +1.301 | 114
6 | Daniil Kvyat | Toro Rosso | 1m19.635s | +1.474 | 77
7 | Sergio Perez | Racing Point | 1m19.944s | +1.783 | 30
8 | Valtteri Bottas | Mercedes | 1m20.127s | +1.966 | 69
9 | Lewis Hamilton | Mercedes | 1m20.135s | +1.974 | 81
10 | Nico Hulkenberg | Renault | 1m20.980s | +2.819 | 64
11 Daniel Ricciardo | Renault | 1m20.983s | +2.822 | 44

There’s some good news, at last, on the horizon for Williams with the team’s car set to fly overnight to arrive in Barcelona in the early hours of Wednesday morning, having missed the start of pre-season testing…

Delays in Williams' production schedule meant the FW42 wasn’t ready for the team's planned shakedown on Saturday nor the opening two days of running in Spain.

They only fired up their car on Sunday night, but after significant work behind the scenes, the new machine looks set to leave Grove later today, bound for Barcelona.

ANALYSIS: Williams: Why is their car late to F1 testing?

There will still be a lot of work to do before the car is ready to go, so Williams believe it is “unlikely” they will be out on track on Wednesday until after lunch.

Williams said in a statement: “Out car looking likely to arrive at the circuit between 4-5am tomorrow (Wednesday) morning.

“Obviously there will still be a fair amount to do but we will be working as fast as we can. Unlikely to run before lunch though.”

Valtteri Bottas has noticed an improvement with the balance of the W10 after another mammoth testing stint for Mercedes.

After piling up 150 laps on the opening day at the Circuit de Catalunya, the reigning champions were back to add another 163 laps on day two.

Five-time World Champion, Lewis Hamilton, had a tricky start to proceedings in the Barcelona cold on Tuesday morning but was still happy with his work as he went under the radar in P10 with 74 laps.

“It’s been a good day overall,” Hamilton said via the official Mercedes website.

“It was quite cold in the morning, so switching the tyres on was a little bit tricky, but it seemed like a few people had similar issues.

“We were focusing on working through our run plan and we got through everything we wanted.

“It’s good that we’re getting in a lot of mileage and we will try to increase that over the next days as we continue to discover the characteristics of this car.

“That’s the exciting part about it – learning something new and being faced with different challenges.

“Everyone is working so diligently, I’m really happy to be here with everyone for the seventh year in a row and I’m excited for this journey that we’re embarking on.”

Bottas, meanwhile, racked up a further 92 laps in the afternoon, finishing P6 with a best time of 1:19.535 – Mercedes’ best time of testing so far.

“We did a lot of laps today and again managed to complete our run plan,” Bottas added.

“We’re learning a lot about the W10 with each run and we’re building a better understanding of the set-up.

“The car was better balanced than yesterday, but there’s still a bit of room for improvement.

“As you can tell from the lap times, we’ve been focusing on long-run work.

“I’ll be in the car tomorrow morning, so it will be a busy evening for me, taking in all the learnings from today.

“It’s been a pretty normal test so far; fortunately, the car has been very reliable, so that’s good news.”

Williams are on the verge of an outright mutiny against their under-performing technical director, Paddy Lowe, as problems with building their 2019 car threaten to deprive the team of crucial winter testing time for a third straight day.

Even by the British team’s dismal recent standards, events of the past 48 hours have been beyond parody. At a time when Williams expected to be fine-tuning their machine ahead of next month’s opening grand prix in Melbourne, engineers have instead been kicking their heels at a hotel near the Circuit de Catalunya, with the car still stuck at their Oxfordshire headquarters.

With the car not due to arrive here in Barcelona until the early hours of Wednesday morning, Williams staff were working through the night just to ensure that it could be ready for the afternoon session. After the cancellation of last week’s planned shakedown of the Williams FW42, as well as the loss of two-and-a-half days of testing, patience with Lowe, the team’s beleaguered technical chief, is at breaking point.

Lowe, who presided over a nightmarish 2018 campaign in which Williams finished bottom of the constructors’ standings, has now failed even to deliver a car to the start line on time. His fall from grace has mirrored Williams’ own: just over two years ago, Lowe was still Mercedes’ top engineering guru, a central figure in the success of Lewis Hamilton, but he has since become the fall guy in the decline of one of British motorsport’s greatest companies.

There is understood to be fury within Williams not just at the car’s shortcomings, but at Lowe’s inability to accept responsibility. While Sir Frank Williams, the team’s founder, has been personally overseeing development work at the Grove factory, day-to-day management rests in the hands of his daughter Claire, the deputy team principal.

Next month, a behind-the-scenes documentary on Formula One will be aired on Netflix, showing previously unseen footage of Williams tearfully questioning her credentials to lead the team during last season’s Monaco Grand Prix.

In 2018, Williams collected a mere seven points from 21 races, and there is little optimism about a turnaround this year. The team invested great hope in their driver line-up, having paired Poland’s Robert Kubica, returning from a potentially career-ending rally accident, with 21-year-old British rookie George Russell, but the problems with the car appear too deep-rooted to surmount any time soon.

Publicly, at least, Russell is emphasising his team’s capacity to stage a revival. “Everyone is working as hard as possible to get it sorted,” he said. “I don’t think it will compromise us too much, to be honest. Winter testing is one thing, but once you get racing it’s a completely different story.”

On the track in Barcelona, Ferrari continued to set an ominous benchmark, with Charles Leclerc almost a second quicker than his closest pursuers. For Mercedes, hoping to emulate Ferrari’s record of six consecutive championships, the challenge could not be greater.

While Sir Frank Williams, the team’s founder, has been personally overseeing development work at the Grove factory, day-to-day management rests in the hands of his daughter Claire, the deputy team principal.