For Nico Rosberg the task is straightforward. It does not require him adding to his nine victories this season. He just needs to finish second twice and third once. The German insists he is still racing for wins but the temptation to play it safe must come in.
Lewis Hamilton's situation is more complicated. If he wins all the three remaining races, a very tall order, then he needs Rosberg to finish one fourth or lower, or two of them in third.
How will Mercedes handle it?
As they have done for most of the season: no team orders, but also no free reign for their drivers to choose whichever strategy they like to try and gain an advantage over the other.
The team has a series of "rules of engagement", written down and shared internally, which they expect Hamilton and Rosberg to abide by. Toto Wolff, the team boss, has said a number of times they have no plans to relax these even now both championships have been secured.
Who does the sport want to win?
There is a split verdict on this one. Some believe it is better for the narrative to have a different world champion heading into 2017. It would also break up Hamilton's period of dominance.
But the counter-argument, put most forcefully by Bernie Ecclestone, the sport's supremo, is that a Rosberg championship does little to promote the sport. Put bluntly, Rosberg is "boring", in Ecclestone's view.
At the moment you can see where the 85-year-old is coming from. In his public engagements, Rosberg is almost deliberately drab as he seeks to maintain his singular focus on taking one race at a time. But perhaps if he does win a maiden title, we will see an outbreak of emotion. That would be Ecclestone's hope.
In a way Rosberg deserves it purely because of the resilience he has shown over the last three years. It takes a lot to keep coming back against a team-mate as strong as Hamilton, improving all the time.
Who is under more pressure?
Fractionally Rosberg, although he is doing a mightily good job of not showing it. He is well in the lead and it certainly is his championship to lose. Whereas Hamilton can go out, give it his all, without now being expected to win.
That said, Hamilton has never lost to Rosberg over the course of a season and it would be a dent to his reputation if he did so, despite all the reliability problems he has faced.
Can anyone else get involved?
Highly unlikely. Every weekend people in the sport get far too excited about Red Bull being able to challenge for victory, but they still lack the speed to take it to Mercedes in a straight fight.
Hamilton's best chance of someone getting in between him and Rosberg is in Brazil, when sudden downpours can turn the race on its head.
Who has better form in the final three races?
The only time the pair have raced in Mexico City came last year, and Rosberg was dominant. There were extenuating circumstances. Hamilton had just clinched a third title and was burning the candle at both ends. He stopped applying himself properly. But Rosberg will marginally be the favourite there.
In Brazil too, Rosberg has won the last two years, while Hamilton has never recorded a victory at the circuit. Abu Dhabi, the final round, is harder to read, with both winning there since they first fought for the title in 2014.
What will decide the title?
In all probability, a mechanical issue one way or the other - or lack of - will be the decisive factor. It is hard to see Hamilton finding a way back unless Rosberg retires with the sort of engine failure he suffered in Malaysia. Equally if Hamilton has another problem, his chances of taking the title are finished.
Either would be Mercedes nightmare scenario. They have already taken so much criticism for unreliability interfering so heavily in the title race. Any more - particularly on Hamilton's car - and the chorus of disapproval from fans online will be deafening.
Which way will it go?
Something remarkable will need to happen for Rosberg not to win the championship. In a car as dominant as the Mercedes, it takes a lot not to finish a race at least second, which is all he has to do. Hamilton can still be at his brilliant best and fall short.
Making predictions in this topsy-turvy season has been a perilous task - who would have thought after the summer break that Hamilton would find himself in this position - but Rosberg has to be the overwhelming favourite.