Lewis Hamilton has admitted he lost sleep over Mercedes shock slump in Malaysia GP Practice - only for qualifying to deliver a dream result for the world championship leader and a nightmare for title rival Sebastian Vettel.
Hamilton will start Sunday's race, underway at 8am live on Sky Sports F1, 19 positions ahead of Vettel following a qualifying hour of unexpected drama at Sepang.
While an engine failure condemned Vettel to last on the grid, Hamilton, a distant sixth in Friday practice and just fourth in Q2, secured one of the most unlikely pole positions of his career with a bolt-from-the-blue lap at the start of Q3.
"We had such a difficult day yesterday, it was difficult to know where we stood," Hamilton said. "I didn't sleep very well last night as we didn't know if we would fix the issue.
"That first Q3 lap I don't really know where it came from. I'm surprised to be up here."
So, too, it seemed were Mercedes themselves with the team attributing the unexpected pole position, secured by less than a tenth of a second over Kimi Raikkonen, to the 'Hamilton factor'.
"This was a Lewis lap," said non-executive chairman Niki Lauda. "I think it is more a driver lap than the car."
Concurring Team boss Toto Wolff added: "A blistering lap, he put it all together, but we are left with some confusion because our car wasn't good. Maybe we shouldn't underestimate the driving factor."
Hamilton on pole position, Vettel last
Starting grid for Sunday's race
Vettel to start from the back of the grid
Mercedes still looking for answers
Mercedes' confusion stemmed from their mysterious struggles in Friday practice which resulted in Hamilton and team-mate Valtteri Bottas splitting their approach towards the team's new aerodynamic package. While Bottas continued to use the new kit, Hamilton reverted to the parts he had used previously this season.
The Englishman revealed his crew had worked until 2am on Saturday morning in a bid to rectify the issue.
"We came with an upgrade that was meant to be better but we were unsure yesterday as we were so far back," said Hamilton.
"Before Qualifying I was thinking about going back onto the new one as Valtteri seemed very happy on it and I didn't want to carry a penalty - you want every little millisecond that you can get. But there wasn't really enough time so we had to stay with it and it's also a risk changing the car again."
Bottas was only fifth, almost seven tenths adrift of Hamilton. "We did end up with completely different cars to Lewis and at the end it seemed to be working for him and not so well for me," said the Finn.
But Bottas has struggled for form since the summer break and Saturday's deficit was also consistent with a gap of over half a second to Hamilton in every qualifying session since the season resumed in August.
"I don't think it's the upgrade issue [for Valtteri]," Wolff told Sky F1. "I think we are going to run it in Japan, all the data says it is good."
Hamilton ready for tough race
Despite defying pre-qualifying expectations by landing pole position, Hamilton is wary of the challenge likely to be presented in Sunday morning's race when he will start alongside Raikkonen on the front row and just ahead of Max Verstappen.
"Red Bull have really stepped up their game in the last race and coming here," said Hamilton. "It's great to see them performing so well and we want them to be closer. I was hopeful they would be quicker today but without a doubt tomorrow they will be on our tail."
With Vettel at the back of the field, Raikkonen will lead Ferrari's charge after missing out on pole by a mere 0.045 seconds.
"It's painful when you get that close," said Raikkonen. "We were quite happy all day in qualifying but we can always improve. We hope Seb will make a good recovery but it's not going to change my race."