The renewed threat Hamilton faces in Brazil

His fourth Formula 1 world championship duly sealed in Mexico, Lewis Hamilton has come to the Brazilian Grand Prix determined to avoid the kind of dip in form he suffered after clinching his third title at the back end of the 2015 season, which helped Nico Rosberg win the final three races that year and set up his own championship charge the following season.

Hamilton has so far made good on his promise to "keep the pressure up exactly the same as it's been all year" this time around, having admitted his focus dropped after clinching the title in '15.

Hamilton was fastest of all in both Friday practice sessions for the 2017 Brazilian GP at Interlagos, suggesting he is still very much "in the zone" that has prevented the clinching of his fourth championship from properly sinking in yet.

There also seems to be no let up from Hamilton's Mercedes team, which has dominated at this circuit for each of the past three seasons, locking out the front row of the grid comfortably and finishing one-two each time.

Kimi Raikkonen's Ferrari was over half a second adrift of Hamilton in the cooler and faster first practice session, when some teams - Mercedes in particular - were experimenting with 2018 development parts.

In the slower, hotter, but more representative running of the afternoon, Mercedes' advantage was reduced but very much still prevalent.

Pure pace ranking (FP2)

1. Mercedes (Hamilton) 1m09.515s
2. Red Bull (Ricciardo) 1m09.743s
3. Ferrari (Vettel) 1m09.875s
4. Force India (Ocon) 1m10.306s
5. Williams (Massa) 1m10.373s
6. Renault (Hulkenberg) 1m10.396s
7. McLaren (Alonso) 1m10.655s
8. Haas (Grosjean) 1m11.300s
9. Toro Rosso (Gasly) 1m11.422s
10. Sauber (Wehrlein) 1m11.857s

Amid his impressive run to this fourth title, Hamilton has had to fight off first the resurgent Ferrari and Sebastian Vettel, who pushed Hamilton hard until Ferrari's season imploded in that run of three wretched races from Singapore to Japan, where Vettel scored just 12 points while Hamilton fell only seven shy of a maximum.

When Vettel has not been the one carrying the fight to Hamilton, latterly it's been Red Bull ace Max Verstappen applying the pressure. The Dutch star has not been a title contender of course, but he has won two of the past four grands prix, and is F1's top-scoring driver since he beat Hamilton to victory in Malaysia.

Amid the euphoria of his title victory last time out in Mexico, Hamilton admitted he would need to raise his own game in response to Verstappen's and Red Bull's improving form, after Verstappen blitzed the field unchallenged at Mexico City.

But Vettel and Verstappen are not the only two Hamilton needs to worry about. Mexico also represented the beginning of a return to form for a driver who starred earlier in the season, and was in title contention heading into the August summer break, before falling away badly thereafter.

With Verstappen and Vettel expecting Mercedes to be away and gone, it will most likely come down to a straight fight between Bottas and Hamilton

Hamilton's Mercedes team-mate Valtteri Bottas now looks right back on form again, having recently endured what he called the worst period of his career.

Until Mexico, Bottas hadn't managed to qualify within 0.3 seconds of Hamilton since the summer break. But in Mexico Bottas was just 0.024s off his team-mate's pace in qualifying, and although he finished well behind Verstappen in the race, it was still Bottas's strongest overall performance since Hungary.

Confidence somewhat restored, Bottas now looks to be Hamilton's closest rival for victory in Brazil. The Finn was just 0.127s slower than Hamilton in first practice and closed that gap to just 0.048s in the second session.

Bottas looked competitive over the longer runs too, only a tenth per lap off on an average of their five best on the super-soft tyre in the morning, and within two tenths per lap over their respective super-soft long runs in practice two.

Long run ranking (super-soft)

1. Red Bull (Verstappen) 1m13.113s (11 laps)
2. Mercedes (Hamilton) 1m13.359s (15 laps)
3. Ferrari (Vettel) 1m13.467s (18 laps)
4. McLaren (Alonso) 1m13.763s (9 laps)
5. Force India (Perez) 1m13.818s (7 laps)
6. Renault (Hulkenberg) 1m14.324s (11 laps)
7. Williams (Stroll) 1m14.354s (16 laps)
8. Sauber (Wehrlein) 1m14.646s (6 laps)
9. Haas (Grosjean) 1m15.122s (4 laps)
10. Toro Rosso (Gasly) 1m15.191s (14 laps)

Long run ranking (soft)

1. Mercedes (Hamilton) 1m12.612s (8 laps)
2. Ferrari (Vettel) 1m12.993s (4 laps)
3. Red Bull (Ricciardo) 1m13.365s (9 laps)
4. Force India (Ocon) 1m13.677s (13 laps)
5. Renault (Hulkenberg) 1m14.027s (9 laps)
6. McLaren (Vandoorne) 1m14.268s (13 laps)
7. Williams (Massa) 1m14.425s (20 laps)
8. Sauber (Wehrlein) 1m14.670s (5 laps)
9. Toro Rosso (Hartley) 1m14.827s (14 laps)
10. Haas (Grosjean) 1m14.839s (4 laps)

"For us it was a positive day," said Bottas. "Everything started pretty well - low-fuel, high-fuel runs, it was all good and we tuned in the set-up. Every change we made seemed to go in the right direction. I think both of us can still find lap time, so I'm expecting a very tight qualifying tomorrow."

The challenge for Bottas will be finding more pace on the soft compound over the longer runs. On this tyre he was half a second per lap off Hamilton's pace, and more than a tenth per lap slower than Vettel's Ferrari.

Vettel only did four representative laps at the end of the session on the soft tyre, so perhaps his pace flatters the Ferrari slightly. Team-mate Kimi Raikkonen's run was almost three tenths off Daniel Ricciardo's effort for Red Bull, which in turn was 0.244s per lap off Bottas.

Sub-1m13s averages by Stoffel Vandoorne and Felipe Massa on the super-soft tyre at the end of the session, over a very short number of laps, were not representative. Verstappen's table-topping effort at least took place over a much more serious range of laps, but with the caveat that he was out of sequence with the other frontrunners when he made it, so most likely on a lighter fuel load than they were.

Given it was a similar story for Vettel on the soft tyre, and allowing for the usual caveats relating to engine modes, fuel loads and set-up experiments, it's probably safe to say Bottas has some breathing space over his non-Mercedes rivals at present.

Vettel certainly doesn't feel he is in serious contention at this circuit, even though he split the Mercedes drivers over the afternoon long runs on both tyre compounds.

"Mercedes seems to be the quickest and then it's very close between Red Bull and ourselves," was Vettel's verdict. "Car-wise, we can fine-tune the balance and that should help us get the pace up for qualifying, and also for the race, but it will be tough to beat Mercedes. They look very quick in all conditions and on all tyres."

There were similarly downbeat noises coming from the Red Bull camp, despite Verstappen's encouraging pace on the super-soft tyre.

Reliability concerns with the Renault engine at high altitude, which wreaked havoc in Mexico, have forced Red Bull to play it safe on power modes so far, and even with the unit cranked up further, team boss Christian Horner and his drivers do not expect to be a threat for pole in the way Verstappen was a fortnight ago.

Bottas seems to have ingested the lessons of those difficult moments and come out stronger

"At the moment I don't think so," was Verstappen's response when asked whether he could challenge for a place on the front row of the grid in qualifying.

"The base [set-up] was OK, not as fast as Mercedes, but hopefully when we make some changes to the car it will be better - the super-soft feels OK on the long run, but on the short run it was overheating too quick.

"If we want to beat Mercedes we need to make a step. We need to be in front to be able to challenge them. We know in qualifying they can step up their engine a bit more, so we need to be at least at the same speed or faster in the final practice."

With Verstappen and Vettel both expecting Mercedes to be away and gone on a circuit that features large parts of the lap spent at full throttle, it will most likely come down to a straight fight between Bottas and Hamilton if the weather remains dry.

The lack of long-run pace on the soft compound will be of concern, and Bottas will know that if he underperforms in qualifying like he has done consistently pre-Mexico City, a lap of Interlagos is short enough for in-form drivers such as Vettel and Verstappen to take full advantage.

But there is little else for him to be worried about right now. Mexico City was the sort of circuit at which Bottas has generally shone this year - low grip, smooth asphalt, a place where it is difficult to overheat the tyres and which rewards his dynamic driving style at low speed.

Interlagos is generally harder on the tyres, with longer-duration corners in rapid sequence, combined with several low-speed traction zones that make it tough to keep the rubber from overheating - especially in the high track temperatures prevalent on Friday.

That is something Bottas has found difficult to keep under control this year - especially on the super-soft compound, which he has described as his weakest tyre. This is the most encouraging news for Bottas - that he seems to have ingested the lessons of those difficult moments in the second half of this season and come out a stronger driver.

"If we look at the issues I've been having, this circuit should be quite bad for me, so I think definitely I've managed to learn a lot from those tricky days," he says. "Looking at today, the performance seemed OK, and I'm sure we can do a better job as a team, and me as well, tomorrow."

He will need to. Hamilton is so far showing no signs of letting up following his title win, and seems determined to close out the season with two more race victories.

Bottas could really use the extra points in his own mission to beat Vettel to second in the standings, but it looks as though he won't get any unprompted presents from Hamilton.

Bottas is going to have to earn it. So far, though not yet in the ascendant, he looks right in the hunt again - much more like the driver that won two of the first nine races, and was a title contender until his post-summer spiral into self-doubt.

It is good to see him coming out the other side and getting his act back together. Nevertheless, Bottas is going to have to dig deep to defeat Hamilton in Brazil. F1's newest four-time world champion has rarely looked harder to beat than he does right now.