After an unpredictable 2020 Formula One campaign ended in wholly predictable fashion, the world's best drivers are back for more in 2021.

The coronavirus pandemic delayed the start to last season and prompted serious surgery to the planned race calendar.

At the end of it all, though, Lewis Hamilton and Mercedes again walked away on top of the pile.

As so often in recent years, the task for the rest of the grid this coming year is simply to stop the reigning champion and his Silver Arrow.

While that is easier said than done, of course, the signs in pre-season are promising.

Will testing preparations derail Mercedes in the opening weeks? We are about to find out, as the Bahrain opener is just days away...

MORE HAMILTON AND MERCEDES DOMINANCE?

Hamilton's title in 2020 was his seventh, tying Michael Schumacher's competition record. A new benchmark is on the horizon if the Briton can repeat his success.

That is not the only landmark in Hamilton's sights, either: with 95 wins and 98 pole positions – both F1 highs – he can surely look forward to a pair of century celebrations this year.

But even if this is to be another sublime season for the 36-year-old, he surely will not find it as straightforward as last year.

Hamilton shut out the noise surrounding his future to claim 11 victories in 2020, yet the new contract he belatedly signed at the end of the campaign keeps him with Mercedes only until the end of 2021.

That spells another 12 months of uncertainty for the sport's premier driver, who also does not yet appear entirely at home in the new W12 car.

The Silver Arrows recorded only 304 test laps in pre-season – the fewest of any team – and may require Hamilton and Valtteri Bottas to learn on the job if they are to extend their record-breaking streak of seven straight constructors' championships.

WHO CAN CHALLENGE THE DEFENDING CHAMP?

Mercedes team-mate Bottas has finished second to Hamilton in the past two seasons, but it would be a tough ask to expect him to outperform the 'GOAT' in the same car – even before considering potential issues with that machine.

No, if Hamilton is to be dethroned, Red Bull look the best bet.

Max Verstappen is undoubtedly the chief threat at the Austrian outfit, having qualified ahead of his team-mates on 36 of 38 occasions since Daniel Ricciardo departed (including a 17-0 record against Alex Albon in 2020).

Indeed, Verstappen – third last year – had the fastest lap time in testing, his effort of a minute and 28.960 seconds in Bahrain putting Red Bull on top in pre-season for the first time.

The Dutchman is pessimistic, though, saying: "[Testing] doesn't say anything about pure performance.

"I know people are excited and think we are just saying this, but Mercedes are still the favourites. How can they not be when they have won seven world championships in a row?"

Ferrari can never be counted out, but they are starting a season with two drivers yet to win a world championship (Charles Leclerc and Carlos Sainz) for the first time since 2007, when Felipe Massa and Kimi Raikkonen lined up for the Scuderia. Of course, that year ended with Raikkonen being crowned champion.

ELSEWHERE...

There is no shortage of intrigue away from the top teams, with two big names returning to F1 – albeit only one of the two drivers having previously raced at this level.

Former champion Fernando Alonso is back, joining the rebranded Alpine team, formerly Renault – where the Spaniard won two titles.

Alonso's most recent race win came in Ferrari colours at the 2013 Spanish Grand Prix, since when he has gone 110 events without victory.

If Alpine can be competitive and Alonso belatedly returns to the top step of the podium later in the season, he could break Raikkonen's record of 114 grands prix between triumphs (2013 to 2018).

The 39-year-old needs only three podiums to reach 100 in F1.

At the other end of the spectrum, Mick Schumacher is the familiar name but new face at Haas, forming an all-rookie line-up alongside Nikita Mazepin, his F2 title rival last year.

Schumacher, who won that championship, will debut at Bahrain eight years, four months and three days after father Michael's final race in Brazil in 2012.

Michael was also 22 when he made his F1 bow, although Mick will be seven months and 16 days younger.

Ricciardo has joined McLaren, who are 12 podiums shy of 500, and Aston Martin are back for the first time since 1960, replacing Racing Point and bringing in Sebastian Vettel.

Meanwhile, there will be increased attention paid to Williams' George Russell, who impressed when given a chance with Mercedes at Sakhir 2020, qualifying second and finishing ninth.

Pierre Gasly believes Ferrari could be the team to watch in the 2021 Formula One season even though Mercedes are likely to finish "clearly on top".

The Scuderia managed just three podium finishes through Charles Leclerc and Sebastian Vettel last year as they came sixth in the constructors' championship.

AlphaTauri were just 24 points behind them, their season buoyed by a remarkable grand prix win for Gasly in Monza.

However, testing ahead of 2021 has offered glimpses of a better future for Ferrari following their worst season in four decades. Carlos Sainz recorded the third-fastest time last Sunday in Bahrain, while he and Leclerc are each said to be happier with the handling of the car after problems with straight-line speed last year.

Gasly, who has spoken privately to Leclerc about Ferrari's progress, believes the team are keeping their cards close to their chest in terms of their progress during the off-season.

He told Stats Perform News: "I think Ferrari are kind of hiding and not showing too much. Compared to last year I think they are clearly better.

"I discussed it with [Charles] Leclerc after the test and we exchanged a couple of messages, talking but not too much, just trying to [laughing], have an idea!

"I think we are close to each other. I don't know if they are ahead of us or if we are slightly ahead. But they have clearly made a step forward. 

"I think McLaren seem to be a very strong opponent and competitor at the moment, especially with a Mercedes engine. They seem to have managed to put a strong package together.

"Then at the top, we will see what happens between Mercedes and Red Bull; it is very difficult to say and make any conclusion. Mercedes had a pretty difficult test, with some reliability issues, but we know how strong they are as a team so I wouldn't be surprised to see them clearly on top."

The new season begins in Bahrain on March 28.

Charles Leclerc has been putting in the hours to ensure Ferrari bounce back from their worst season for 40 years.

In 2020, Leclerc finished eighth in the drivers' standings, with 98 points and two podiums to his name.

Even that fairly meagre return meant he fared better than Sebastian Vettel, who had 33 points and a solitary podium down in 13th.

The former world champion has joined Aston Martin for 2021 following the lowest points total of his career, with Carlos Sainz in place as Leclerc's new team-mate.

The Monegasque was cautiously optimistic at Friday's season launch, having left few stones unturned during the off-season, but he knows it is foolish to predict how a wounded Ferrari might fare against Formula One's other heavyweights.

"There has been a lot of work. We have been pushing quite a lot," he said.

"It always looks positive on paper but then we need to see what the others have done as a step.

"I have never been in [the] Ferrari [factory as much] as before this season. We have been doing quite a bit of tests with the old car. I feel very ready.

"I have been working in a similar way as in the past, trying to understand what my weaknesses were last year.

"I still believe tyre management is something I should push. I improved a lot last year and I hope there will be another step this year."

Last month, Leclerc was forced to put such intensive preparations on hold as he self-isolated having tested positive for coronavirus.

However, he offered assurances that there have been no lingering effects.

"COVID did not hit me that bad," said the 23-year-old. "I did some physical tests to make sure everything came back to normal and that is the case."

Having comprehensively out-driven Vettel as the younger man, Leclerc anticipates a different dynamic when Sainz – fresh from two seasons at McLaren – joins him on the grid for the 2021 opener in Bahrain on March 28.

"It is very clear we need to push for the team," he added.

"Carlos wants to beat me and I want to beat him too. We will try to be careful when we fight each other on track.

"What is most important is we separate what happens on the track and off the track. It is a fine line that every team-mate needs to find.

"Carlos is very competitive but he is also here for the benefit of the team, as I am. We will have to play it smart on that one."

Ferrari driver Charles Leclerc has tested positive for coronavirus, the team have confirmed.

The 23-year-old was already isolating having been in close contact with someone who had contracted COVID-19.

Ferrari said Leclerc is isolating at home in Monaco and is displaying mild symptoms.

A team statement read: "Scuderia Ferrari Mission Winnow driver Charles Leclerc has tested positive for COVID-19.

"In accordance with the team's protocols, Charles is tested regularly and yesterday, the result from his latest test came back positive. 

"Charles notified us immediately and has informed everyone he has been in close contact with in the last few days.

"He is currently feeling ok with mild symptoms and is now self-isolating at home in Monaco."

Leclerc added on his Instagram stories: "Hello guys. I hope you are all staying safe.

"I want to let you know that I have tested positive for COVID-19. I am regularly checked according to my team's protocols.

"Unfortunately, I learned that I have been in contact with a positive case and immediately went into self-isolation, notifying anyone I had contact with. A subsequent test I took has come back positive.

"I am feeling okay and have mild symptoms. I will remain in isolation in my home in Monaco in compliance with the regulations set by the local health authorities.

"Stay safe and take care."

World champion Lewis Hamilton tested positive towards the end of the 2020 F1 season, while Lance Stroll and Sergio Perez have also previously missed time due to coronavirus.

Ferrari do not regret their failure to sign Lewis Hamilton for the 2021 season as they are confident Charles Leclerc can challenge the Formula One champion.

Hamilton has won six of his record-equalling seven world championships with Mercedes, although he has not yet committed to the Silver Arrows for the coming campaign.

A resolution is expected soon, but links to rivals Ferrari have never been far away.

A blockbuster move will not materialise on this occasion, however, as the Scuderia have secured Carlos Sainz Jr next to Leclerc in their 2021 line-up, replacing Sebastian Vettel.

And team principal Mattia Binotto is confident they have made the right move.

He told Sky Sports: "I don't think there will be regret because, at the end, when we took some decisions, we took them thinking they were the right decisions and today we have a fantastic driver like Charles, where we invested a lot as Ferrari.

"I think he's got a lot of talent. If he's got the right car, I'm pretty sure he can challenge Lewis Hamilton.

"We've made our choices and I think, together with Carlos, we are very strong. I don't think there will be any regret."

Although Leclerc - fourth two years ago with two wins to his name - would appear the obvious Ferrari contender, Binotto is not naming a "number one".

Sainz finished seven points better off than his new team-mate in 2020 while still with McLaren.

"There is not a number one and number two," Binotto said. "They will have equal opportunities - certainly at the start of the season. I'm pretty happy then that they are free to fight.

"I think what we have to do as usual is to optimise the team points, and when you optimise the team points, normally you are optimising the drivers' points as well. Team points is the number one.

"Later in the season, let's see how things will progress, let's see what objectives individual drivers can maybe achieve and if we need to adopt a different strategy, but at the start of the season, they will be free to fight."

Carlos Sainz compared Ferrari and McLaren to LaLiga heavyweights Real Madrid and Barcelona, and is confident of a successful transition to the Scuderia. 

The Spaniard spent the past two seasons at McLaren, making the podium on two occasions, but is Ferrari-bound for 2021, replacing Sebastian Vettel.

Sainz spoke about how the objective for both teams is to cut the gap to dominant Mercedes, while he feels the fact he will have raced for both teams proves he is doing something right in his career.

Asked by AS if racing for Ferrari is like playing for Real Madrid, the team Sainz supports, he replied: "It's one way of saying it…but McLaren is Barca, which is also a very good team to be on. 

"It cannot be compared, because in addition both are in a restructuring to try to dethrone Mercedes in the future. 

"But they are the two best teams in history and when you go from one to the other it means that you are doing something right in Formula One."

At Ferrari, Sainz is joining a team where the pressure is always on to be a success and internal politics have historically always been a lingering presence in the background.

But Sainz is confident of being able to bring a harmonious atmosphere like the one he was part of at McLaren.

"That I managed to do it at McLaren means I can do it at Ferrari. If I could create a good team, generate good dynamics at McLaren, why not do it at Ferrari? I can do it," he added. 

"I like the people out there, I like Mattia [Binotto, Ferrari team boss] and I like what I see, what we have talked about. 

"There was no hesitation when it came to signing the contract and going forward. In my head there is no possibility that this environment and similar situation cannot be generated. 

"If I could at McLaren, I can at Ferrari."

Sainz's predecessors at Ferrari Vettel and Fernando Alonso arrived with huge reputations as two of the most gifted drivers of their generations and with world titles to their name.

Neither man was able to end Ferrari's wait for a champion dating back to 2007 but Sainz believes it is wrong to judge their success at Maranello based on titles.

"They leave with a few victories and podiums, if you call that going empty…I only have two podiums," he said. 

"Are they leaving without a championship? Yes. But the same has happened to nineteen drivers, every season for the last 10, when Red Bull or Mercedes have dominated. 

"There are nineteen drivers a year who have gone empty, but I do not include those who have raced for Ferrari. Nobody leaves Ferrari empty."