Lewis Hamilton claims it is "no secret" the new Formula One regulations have been introduced to slow Mercedes, but he was encouraged by their opening qualifying session of the season.

Changes to aerodynamic regulations for 2021 have had a great impact on the reigning champions' low-rake chassis, the Silver Arrows say.

Mercedes have won the past seven constructors' championships, yet Red Bull led the way in pre-season testing.

The fastest lap belonged to Max Verstappen and the same man took pole on Saturday at the season-opening Bahrain Grand Prix.

But Hamilton was only 0.388 seconds back in second and that performance spells good news for the Briton, with all 16 Bahrain winners coming from the first two rows of the grid but only seven of them qualifying on pole.

Meanwhile, Verstappen has retired three times at this event and four times at the Sakhir track.

Hamilton remains very much in contention, despite feeling the rules have been designed to hurt his team.

"It's no secret. The changes, of course they've been done to peg us back," he said. "We've had the changes last year to our engine to do the same thing.

"That's okay. We love a challenge, we don't look down on these things. We just work hard to do the best that we can, and that's what we'll do."

But Hamilton was not amused by a request for him to analyse where Red Bull are now better, as Verstappen - having ended last year with a win - targets back-to-back triumphs for the first time in his career.

"Really? I don't want to tell you what our problem is," Hamilton said. "They're just faster."

With Silver Arrows team-mate Valtteri Bottas qualifying third, the top three - Verstappen, Hamilton, Bottas - are on course to become the first trio to appear on 15 podiums together.

Although Verstappen is still in the lead, this Mercedes challenge seemed improbable for Hamilton just days ago.

"I think this is a really good step forward for us coming this weekend," he said.

"We thought it was double the gap that you see today. That's down to some really fantastic work from the men and women back at the factory.

"Of course we want to be first, but we knew that it was going to be a challenge, we knew from day one on track really that Red Bull was going to be faster than us.

"We knew we had a bit of an uphill slope to climb. I'm just proud of everyone's efforts."

Elsewhere, two former champions had vastly contrasting fortunes after offseason moves.

Three-time Bahrain winner Fernando Alonso is back in F1 with Alpine Team, formerly Renault, where he won two world titles.

And his second debut was a success as he reached Q3 for the first time since Monaco 2018 and claimed ninth on the grid.

"It was good," said Alonso, who won this event on the previous two occasions it opened a season. "I think we have to be pleased with the qualifying.

"I was not confident in any of the sessions so far in the weekend - I was struggling a little bit to feel the rear of the car in windy conditions - and now in the qualifying everything was calmer.

"The night situation I think helped us with the cooler temperatures, so I was able to attack and feel the car a little bit better and it was fun."

On the other hand, Sebastian Vettel was eliminated in Q1 as his second run was hampered by yellow flags prompted by Haas rookie Nikita Mazepin's spin.

No driver has more wins (four) or poles (three) in Bahrain than the former Ferrari man, but his Aston Martin bow did not go to plan.

Vettel will start from 18th and said: "If I panicked now, would it help? If I was really upset?

"For sure, I am upset and angry that it wasn't our fault in a way not to make it through, but we have to take it and do what we can, preparing tomorrow."

Matters could yet get worse for the German, who will appear before the stewards on Sunday for failing to respect the flags, potentially meaning a five-place penalty.

Lewis Hamilton returns to Bahrain four months on from winning an 11th race of a dominant 2020 season knowing Mercedes have plenty of questions to answer from an exciting-looking Red Bull.

It was another season to remember for Hamilton in a campaign disrupted heavily by the coronavirus pandemic, the Briton himself contracting the virus late in the season and missing the second leg of a Sakhir double-header a week later.

By winning a seventh Formula One world title, Hamilton levelled Michael Schumacher's all-time record and also surpassed the legendary German for overall race wins (now 95), and he is now going in search of history.

But the evidence in pre-season suggests Mercedes are set for a titanic tussle with Red Bull, whose exciting line-up of Max Verstappen – the 23-year-old many are tipping to finally go toe-to-toe-with Hamilton – and Sergio Perez will be out to lay down a marker at the Bahrain International Circuit in Sakhir.

Many have suggested that F1's technical 2021 changes have redressed the competitive balance and certainly there was evidence to suggest as such at pre-season testing where Mercedes posted the lowest lap count of any team and Red Bull set the pace on two out of the three days.

We have been here before with Mercedes, though, where some have questioned whether their period of dominance – the Silver Arrows winning the constructors' championship seven years running – is finally over, only for the German manufacturers to turn it on when it matters.

This weekend should give us a clearer indication as to the strength of both teams, but that is by no means the only talking point on the grid...

LAST TIME OUT

Red Bull can certainly take heart from a strong end to the 2020 campaign, which saw Verstappen coast to victory at the Abu Dhabi Grand Prix, a race in which Hamilton finished third after returning from his absence due to COVID-19.

In that race, Red Bull were not necessarily favourites but beat Mercedes in a straight-line fight for Verstappen's second triumph of the season – his first coming in round five at the 70th Anniversary Grand Prix.

Perez can also take plenty of confidence from the fact he triumphed at this circuit for the Sakhir Grand Prix a week after Hamilton's last win of 2020, with a power issue in Abu Dhabi meaning his final outing with Racing Point ended in a whimper.

Valtteri Bottas finished second ahead of Hamilton on that occasion and the Finn knows he has a lot to prove against a strong-looking Red Bull line-up, while McLaren cars finished in fifth and sixth and are fancied for another strong campaign after finished third in the constructors' championship.

WHAT TO LOOK OUT FOR IN SAKHIR

There are plenty of sub-plots in play this weekend after a close-season of change in F1.

Most notable is the return of a legend and the arrival of a rookie aiming to emulate his great father.

Two-time world champion Fernando Alonso is back, racing for the rebranded Alpine Team – formerly Renault where the brilliant Spaniard won his two titles.

Mick Schumacher, son of Michael, has sizeable shoes to fill and will start his career on the biggest stage with Haas alongside fellow F1 rookie Nikita Mazepin.

Sebastian Vettel has a new home after ending his association with Ferrari and will race for Aston Martin, who are back in F1 for the first time since 1960, while the Scuderia signed Carlos Sainz Jr from McLaren to line-up alongside Charles Leclerc for 2021.

McLaren consequently turned to amiable Australian Daniel Ricciardo to partner Lando Norris, with the team starting 2021 12 podiums shy of 500.

TOP FIVE OPTA STATS

- Vettel and Hamilton are the drivers to have won the most races at the Bahrain GP (four), and have taken the most pole positions (three).

- In 2014, Mercedes recorded the first out of their 70 one-twos in hybrid-era qualifying in Bahrain (Nico Rosberg first, Hamilton second). The Germans have achieved 78 one-twos; they are two wins away from reaching Ferrari as the team to have secured one-twos in qualifying most often (80).

- Mick Schumacher will race his maiden grand prix in Bahrain eight years, four months and three days after father Michael's final appearance in Brazil 2012. Both will have started in F1 aged 22 years old, but the younger Schumacher will have done so seven months and 16 days earlier than his dad.

- Sainz will be the third Spanish driver to race for Ferrari. In his maiden race for the Scudería, Alfonso de Portago failed to finish in France (1956), but Alonso won in Bahrain (2010).

- Verstappen has retired three times at the Bahrain Grand Prix (four in Sakhir), more than any other race in his F1 career. The Dutchman has the chance to win back-to-back grands prix in F1 for the first time after 120 races.

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.

Sebastian Vettel is excited to get the 2021 Formula One season underway with Aston Martin, with the former world champion seeing plenty of potential at his new team.

Vettel, a four-time F1 champion, left Ferrari at the end of the 2020 campaign, bringing an end to a six-season stint with the Italian manufacturers.

Charles Leclerc had usurped him as Ferrari's number one driver, and Vettel slumped to a 13th-placed finish in last year's drivers' standings, claiming just one podium finish.

Vettel has now switched to Aston Martin, who have rebranded the Racing Point team to make their F1 return after a 61-year break from the competition. 

The German made no secret of his disappointment at how his final season at Ferrari panned out but is anticipating an exciting debut year with Aston Martin.

"I am not happy with last year in terms of performance – partly my performance – but I accepted it," said Vettel at the unveiling of the AMR21 car on Wednesday, which also featured NFL great Tom Brady and Hollywood star Daniel Craig.

"There are things that didn't go well, but I am looking forward to this year.

"I go racing to win and obviously it's a very exciting project, a new start and a new chapter for the entire team. I'm very much looking forward to it.

"Winning is maybe a bit ambitious straight away, but it's everybody's goal, it's why we go racing.

"Even though I have raced for four Formula One teams and for many years, starting a new season with a new team still gives me a sense of excitement.

"I see potential. I think the team has always been very successful in the past with limited resources, now the regulations in F1 are changing, and with the new launch of Aston Martin coming back, a lot of talented people joining and coming together to this already good group already, I think it's [his arrival is] only an addition.

"So I hope that I can contribute as well, and I think if we keep sharing that joy and passion then good things will follow."

Vettel's Ferrari future was decided before the 2020 season – which was derailed due to the COVID-19 pandemic – had started, yet he claims to have had no doubt that Aston Martin was the right move. 

"As a driver, I have always kept my eye on the competition and this team has consistently impressed me with what they have been able to do without the biggest of budgets," he added.

"So, when Lawrence [Stroll] and Otmar [Szafnauer] approached me last year, and explained what their ambitions were, I was immediately very motivated to join the team.
 
"I love the history of motor racing and Aston Martin is one of the great names of the past, so it is fun to be part of their return to Formula One after an absence of 61 years.  
 
"I have not driven the car yet but I think it looks great. I am really looking forward to getting it out on the track. I am also looking forward to working with and getting to know better everyone in the team, including my team-mate Lance [Stroll]. We will certainly make a big effort to deliver some good results together and have fun doing it."