F1 2018: Hamilton v Vettel - the race for five titles
Lewis Hamilton and Sebastian Vettel will both be hoping to become just the third man to win a fifth Formula One world championship in 2018.
Hamilton prevailed in a battle with Vettel last season as Ferrari finally looked capable of providing a winning driver for the first time since Kimi Raikkonen's triumph in 2007.
The Briton's fourth title came nine years after his first, with his German rival claiming all of his in succession during a dominant stint with Red Bull.
A place in motorsport immortality alongside Michael Schumacher and Juan Manuel Fangio awaits, but who is best placed to achieve it this year?
The case for Hamilton
Mercedes have been untouchable at the pinnacle of F1 for the past four seasons, with Hamilton only beaten to the title by team-mate Nico Rosberg during that period.
It is difficult to envisage the German team's stranglehold over the sport loosening as they came out of pre-season testing with the best race simulations, although those stints were done on only one tyre compound.
Hamilton trailed Vettel in the early stages of the previous campaign but his single-mindedness and determination to prove himself as one of the elite saw him dig in and, following the mid-season break, he overturned a 14-point deficit to the German with a run of six wins in eight races.
It does not appear winning the championship for a fourth time has taken away any of his desire to make himself the man to beat this year.
"I am on the same level as every driver here, but I want to prove that I am above them and that means I have got to work harder than I have ever worked before," said Hamilton.
It will certainly take something special to stop him from proving that point.
The case for Vettel
Vettel heads into this season as the fastest man across both testing sessions in Barcelona.
The German finally got the chance to challenge for a title in a Ferrari last year, with a run of six successive podiums to start the campaign laying the foundations.
His tilt unravelled in the second half of the season; Vettel was caught in a crash involving Raikkonen and Max Verstappen in Singapore and suffered an engine problem in Japan, and Hamilton took full advantage by winning both races.
If Ferrari can avoid reliability issues across an entire season and the 30-year-old does not have the misfortune of being wiped out of a grand prix, there is every possibility he can push Hamilton all the way.
Should Vettel manage to at least stick close to the Mercedes star, he can force his rival into taking greater risks from which he can deliver a punishing blow.
His performance in Barcelona suggests Ferrari have the speed to cause some real problems this year, but it will take a flawless campaign from him and the team to dethrone Hamilton and Mercedes.