Lewis Hamilton has admitted that he had feared another reliability problem during the United States Grand Prix in Austin.
The British driver has suffered from multiple engine failures during the course of the season, which have ultimately derailed his chances of retaining the World Championship title.
Mercedes teammate Nico Rosberg currently sits in top spot and still holds an astonishing 26-point lead over his compatriot, despite finishing behind him this weekend.
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Hamilton commented on the engine problems: "I was just petrified the car wasn't going to make it.
"That's probably the first time in my whole career I have had that weighing heavily on my heart throughout the whole thing."
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The 31-year-old was dealt a major setback at the Malaysian Grand Prix two races ago when he dominated the contest only to succumb to an engine problem, which would have otherwise provided him with a lead in the Driver's Championships, instead leaving him with a 23-point deficit.
Matters were made worse at the subsequent race in Japan, as Rosberg won while Hamilton finished third, extending the lead to a mammoth 33 points.
Only after safely completing the race in Austin, was the Brit able to breathe a sigh of relief.
The World Champion added: "It was the longest afternoon I had probably in my whole career, just hoping the car makes it to the end. Every single lap I was thinking something might happen."
Having cut the gap to 26 points, Hamilton is making strides towards rectifying the situation, but still faces a daunting task to stop his German teammate.
Even if Rosberg finishes second to Hamilton during all of the remaining three races, he will clinch the world title, such being the extent of Hamilton's rescue job.
However, the British driver has vowed to push his competitor to the very finish, saying: "I just want to keep my head down and do the best job possible all weekend and I can't control what will happen behind.
"All I can do is make sure when I leave this season I know I did everything with a full heart."
Winning his 50th career race, Hamilton now finds himself in elite company, alongside Michael Schumacher and Alain Prost, the trio being the only drivers to achieve this feat.
Only one win short of the Frenchman's total of 51 wins, Hamilton seems likely to overtake that record.
Schumacher, on the other hand, has 91 wins to his name which would take some effort on the part of the current champion to reach.
Hamilton, however, is optimistic regarding his chances, saying: "It's kind of very surreal, for sure. I can't believe there are only three of us but hopefully on to bigger and better things."
The 31-year-old also reflected upon his career: "I had completely forgotten it was going to be 50th. It's been a long time coming.
"I know I've mentioned it before, but I have been here for 10 years, I've had lots of ups and downs and lots of great opportunities to work with some incredibly gifted people who have helped me get here today. Then my family as well without whom I woudn't be here today."
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