He had a handful of difficult races, including some bad luck with the timing of safety cars. His new team-mate George Russell built a lead over him in the championship, and people started to snipe from the sidelines, question whether Hamilton was past it, even whether he should have retired.
The truth was that Hamilton was taking the brunt of experimentation with the car on race weekends.
"Literally, I have tried everything," he says. "I've tried every setting you can possibly do. That's what I was doing at the beginning of the year.
"The whole idea of performing at your best and getting the best result each weekend; of course that would be nice, but I was really about problem solving: 'I will sacrifice this session or all the sessions to be able to find more data and information for you.' So that when we go back to the factory they've got a better understanding of what's going on.' But it ultimately hindered some of the weekends."
From about the Canadian Grand Prix in June onwards, Hamilton decided that this approach was not the best, and he began to focus more on performance rather than experimentation. And as he did, the picture began to change.
Russell has had a brilliant season. He is closer to Hamilton on pure performance than any team-mate since Fernando Alonso in 2007, and has very much consolidated his status as one of the brightest stars of the new generation, and a driver more than good enough to lead Mercedes in the future.
But while the average qualifying gap between them over the season is just 0.06secs, if you take only the races from Canada onwards, the margin is 0.175secs.
Hamilton is ahead nine-four on their qualifying head-to-head at races where a fair comparison can be made, and has out-qualified Russell for the last six races in a row. Hamilton, Mercedes engineers say, is better able to cope with the car's unpredictability.
"George, I would say, and his team, they don't experiment the same, obviously. But that's because I've been here for a long time, so I'm willing to take these risks.
"I have the big, deep conversations with people I've been with for 10 years. So, me and 'Shov' [Andrew Shovlin, Mercedes' engineering director] can have arguments, constructive arguments.
"George, it's his first year with the team so he's come in and he's just doing his job to the best of his ability. Very little movement of set-up. I'm doing all the leg-work, back and forth here and there, different wings, all these different things. And I like that anyway.
"If we come into next year and we have a car that we are much happier with, then we can be more focused on that whole… not having to go crazy with set-ups. Then we can have a better battle.
"If he finishes ahead at the end of the season, I don't really feel anything about it. We're not in the championship. We are fourth and sixth. Now, if it was first and second, it's different."
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