Lewis Hamilton insists he never doubted his Formula One world title hopes, despite a tricky start to 2018 as Sebastian Vettel threatened.

The Mercedes star successfully defended the drivers' championship in Mexico on Sunday after a storming second half of the season, but the first few months were not quite so easy.

Hamilton won just three of the first 10 races, missing out on a place on the podium in China and Canada while retiring in Austria.

But the Briton, now a five-time champion, was always confident that he and Mercedes would be able to compete at the business end of the campaign, even if he believes Vettel and Ferrari have had the faster car for much of the year.

"People watching only ever see the tip of the iceberg," Hamilton said. "When you see someone successful on TV, it's obviously without a full description of what they have done to get to where they are. You just see the success that they are having now.

"To perform this way this year - trust me - it has been the hardest season for me.

"To keep raising the bar and racing against a four-time world champion [Vettel] in a really incredible team who were so fast this year - most of the time faster than us - and to have pulled together as a team and turned it around has been a real collective effort from everyone. I am really proud of everyone.

"Honestly, I never stopped believing - that's just how I am wired. I truly believed from the beginning of the year, even when we had difficult races such as Shanghai or Montreal. I never for a moment doubted or lost belief in this team, in my guys or in myself."