How big are Mercedes' problems and can they find their pace in Japan?
What went wrong for Mercedes in Malaysia and whether they could be outpaced by Ferrari and Red Bull again at Suzuka
In world championship terms, the Malaysia GP could be regarded as yet another successful weekend for Mercedes.
They left Sepang with increased leads in the Drivers' and Constructors' Championships and were only denied a pole position-victory double by Red Bull, a team not in title contention.
Meanwhile, Ferrari shot themselves in the foot for the second successive race as engine failures severely damaged Sebastian Vettel and Kimi Raikkonen's weekends.
Scratch just a little beneath the surface, however, and a very different picture emerged.
For the second race in a row, Mercedes were only the third-quickest package. And while a struggle was expected in Singapore, Malaysia felt different because of pre-race expectations they would prosper.
But the world champions were comparatively slow on all three days with Hamilton revealing the team believed they had fallen up to eight tenths a lap behind Ferrari.
"There are some really big problems which I can't really explain to you," said a concerned-sounding Hamilton on Sunday night. "There is a lot of work for us to do. But there's nothing we can do, it's the way the car is.
"We do have some big problems with it. I think it's a fundamental issue with this year's car."
So just what are Mercedes' problems - and how big are they?
Are Mercedes really struggling?
On the face of it, Mercedes' championship positions in 2017 have never been more formidable: Hamilton leads Vettel by 34 points, while the team enjoy a 118-point advantage over Ferrari.
But Mercedes know they're very fortunate to be that far ahead and, in the case of the Drivers' Championship, even hold a lead at all with five rounds to go.
"You cannot look at it and say we have scored more points than Ferrari - we have lost so much pace this weekend," stressed team boss Toto Wolff.
"We were half a second down on Ferrari [per lap] and probably if Max Verstappen had pushed to the end we would have been half a second down on Max."
Mercedes had expected Singapore to prove their one main outlier in the second half of the season, so Hamilton's against-the-odds victory on a weekend Ferrari and Red Bull had threatened to dominate proved an unexpected piece of good luck.
They weren't expecting to have to rely on that level of fortune at Sepang, so the W08's immediate deficit to the same two rivals in last weekend's first dry practice session proved the most abrupt of surprises.
Hamilton and Valtteri Bottas both struggled badly for grip and lapped 1.4 seconds adrift of Ferrari's leading pace, prompting Wolff to describe it as "one of the worst Fridays I can remember". Such were the problems that Mercedes' mechanics worked until 2am on Saturday morning to find a set-up "gremlin" in the car.
Unusually, Mercedes then hedged their bets from Saturday as Hamilton reverted to an older-spec aero kit, while Bottas stuck with the planned Sepang package.
Hamilton's pole position later on Saturday was still wholly unexpected - and, like his Singapore win, it proved highly misleading. Both Wolff and Niki Lauda credited the pole to the 'Hamilton factor'.
"Lewis, what he did today, no one else I think can do that," purred Lauda. "He's fantastic, especially thinking about his lap time here, because the difference he makes [compared] to everybody. It's only Lewis."
And even then, had Vettel's engine not given up on him in Q1, or Raikkonen not snatched a brake to costly effect on his final Q3 lap, Hamilton's best efforts would probably have delivered no better than the second row.
What went wrong in Malaysia?
While the Mercedes W08 has won five more races than any other car this season, the team's 2017 challenger has displayed 'peaky' performance since winter testing. That inconsistent form famously led Wolff to christen the car a 'diva' after a Ferrari-dominated Monaco GP in May.
While slow, twisty circuits like Hungary and Singapore continued to prove Ferrari's domain, Sepang, with its fast corners and two long straights, wasn't supposed to be like that. For Mercedes, it was supposed to be more like Silverstone and Spa, races they won.
But there was one big difference: temperature. Thirty-degree temperatures.
"We need to understand why we underperform on certain circuits and in certain ambient conditions," said Wolff. "I think we have a capricious car that has a very narrow operating window with the tyres. Dipping in and out of the window is the fundamental story of 2017 for us."
In short, Hamilton got the car and tyres in the correct window when the temperatures were slightly cooler during Saturday's qualifying hour, with his pole-winning lap coming just before 6pm local time. But, just as on Friday, the W08 fell back out of kilter again on Sunday when the race took place at 3pm.
After struggling on Friday's long runs, it's also understood that Mercedes dialled some understeer into their cars in a bid to protect their rear tyres. The flip side of that set-up direction was that it compromised handling.
"There is stuff you don't even know about that has been happening through the weekend that is not acceptable for this great team and we all know that and need to work on those areas," said Hamilton.
Hamilton finished second, but was unable to challenge Max Verstappen once the Red Bull overtook him on lap four, while it's likely both drivers would have been beaten by Ferrari had Vettel started at the front and Raikkonen taken the start from second on the grid.
Where has Bottas' form gone?
Mercedes' problems have been compounded by Valtteri Bottas' collapse in form. In the four races since the summer break, the Finn has regressed from title contention to crisis. "It may be the most difficult time of my career so far, in terms of how it feels every time I go in the car," he said on Sunday.
Bottas has been out-qualified by Hamilton by over half a second in every Saturday session since the break and finished Sunday's 56-lap race 56 seconds behind Verstappen and over 40 adrift of Hamilton. As explained above, Mercedes removed the new aero kit from Hamilton's car but kept it on Bottas'. But the Finn's sudden loss of form must have left the team none the wiser about the worth of their Sepang upgrades: Bottas' 0.682 seconds deficit to Hamilton in qualifying this Saturday was almost identical to the 0.682 between the Mercedes team-mates in Singapore. "I'm worried," team boss Toto Wolff told Sky F1.
On one hand, Bottas' regression is good news for Hamilton as it removes one rival from the title-race equation and any doubt about which driver Mercedes ought to support. But it has also removed a major advantage Hamilton had over Vettel: in complete reverse to the start of the year, Raikkonen now looks far more likely to take points off Hamilton than Bottas does with Vettel.
What will happen at the Japanese GP?
"They go to Japan with some big question marks," said Sky F1's Ted Kravitz of a Mercedes team who will want to nip their latest 2017 performance wobble in the bud at Suzuka this weekend.
The turnaround from Sepang to Suzuka may be short, but the figure-of-eight circuit has proved one of Mercedes' happiest hunting grounds since the V6 engine era began in 2014. They've claimed three consecutive front-row lockouts and three consecutive race wins.
"On paper, Suzuka should suit us," predicted Wolff. "There were some question marks over Malaysia - we should have been quicker than we were - but Suzuka should be much more in the window."
A drop of temperature in the region of 10 degrees from Malaysia should help matters, with the configuration of corners at Suzuka also potentially more favourable for the W08.
But Ferrari, who boast arguably the season's best all-round car, and Red Bull, who certainly possess the season's most improved, also have reason for optimism and they'll be buoyed by their Brackley rivals' rare recent signs of weakness.
Make no mistake, Mercedes remain F1 2017's likely double world champions.
But fail to win in Japan and the problems will suddenly start to become big ones.