Lewis Hamilton insists the journey to his sixth Formula 1 title has "no way been the easiest" in his career.

The Mercedes driver officially moved upto second by himself in the all-time list after finishing second at the United States Grand Prix on Sunday, despite losing out to teammate Valtteri Bottas.

It was a moment that merely confirmed the inevitable after a dominant first half of the 2019 season had seen Lewis win eight of the first 12 races and open up a considerable points advantage.

However, while a lack of competition may have made championship No.6 one of his most impressive, Hamilton is adamant that doesn't tell the full story. 

"No way has it been the easiest," he stated post-race in Austin.

"It’s been the hardest year for us as a team. We lost Niki [Lauda] this year, a crucial member and a real pivotal member of our team and the emotional rollercoaster that we’ve been on with losing him, and a race where I didn’t have [race engineer Pete] Bono [Bonnington] here.

"So outside of the car, just trying to remain focused throughout the year, that is the toughest [challenge I've had]."

While Mercedes have also had a superior car over their rivals for much of the season, Hamilton noted how it came after a slow start initially in testing and hasn't lasted until the end of the year.

"This car has not been easy. We started the season honestly going off to Melbourne thinking that we were going to be behind," he recalled. "Mid-point of the season we were behind, and it’s been a real challenge, this second half of the season.

"It’s been the toughest second half of the season that I think we’ve had as a team, fighting against Ferrari and Red Bull, which is great, we welcome that. But, I don’t know, every journey is different. Every year you go through a different rollercoaster ride of emotions to get to where you’re going.

"I wrote something in my post this morning, that each and every single one of us is struggling with something in life.

"Whatever it may be: small, big. I tried to show people that, from the outside, things always look great but it’s not always the case and I am also struggling with lots of different things and battling certain demons and trying to make sure that I’m constantly growing as a person.

"I think yesterday was something that was sent to test me," Lewis added, referring to a tricky qualifying session. "And I was able to do one of my favourite races today, I think. I was really happy with that one."

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The key to Hamilton's success has again been consistency with 10 wins to his name and only three races where he hasn't been on the podium.

And asked by the BBC if he considered 2019 his best year performance-wise, the Briton approved adding he hadn't finished yet.

"I think so. I definitely think so," he replied.

"I think last year was a year of just continuous growth and I think this year has also been continuous growth but I tried to make sure that I started the season as I finished last year, and I think that’s just stayed through the season.

"I think it’s been the best performing year and I think I’m really just trying to… I’m working on a masterpiece and I haven’t quite finished it yet, it takes a long time to master a craft and whilst I feel like I am mastering it, there’s still more to master.

"There’s going to be more ups and downs along the way but I feel like I’ve got the best tools now, to this point at least, to be able to deal with those."