Lando Norris said he was left feeling demoralised for a week after seeing the door virtually slammed shut on his bid for world championship glory.
Norris heads into this weekend's Las Vegas Grand Prix 62 points adrift of Red Bull driver Max Verstappen, with only 86 points remaining across the final three rounds.
Verstappen will take his fourth consecutive title if he outscores Norris on the Strip following the Dutchman's stunning comeback drive from 17th to first at a rain-lashed Brazilian Grand Prix a fortnight ago.
Norris started from pole position but crossed the line a disappointing sixth. And speaking prior to the 22nd round of 24, Norris said: "It was a defining moment for the championship. The door is almost shut.
I was pretty down for a week, there was the realisation that things are out of my control and not within reach
"I was pretty down for a week after Brazil because there was the realisation that things are out of my control and not within reach and that was a tough moment. When your hopes and beliefs are so high, and then for them to get knocked down, that was pretty demoralising and not the best of feelings but you learn to accept that is life.
"I can survive, I can put up a fight, and that is what I will do. But at some point you know it is not going to go your way. You never know. I am not saying it is over and I wouldn't until it is, but it is very far out of reach. I need a lot of luck. I have to win three races, and hope Max fails to finish in those three races."
Norris has failed to convert seven of his eight career pole positions into an opening-lap advantage, and finished 31 seconds behind Verstappen in Sao Paulo, despite starting 16 places ahead of his rival.
McLaren have also provided Norris with arguably the fastest machine on the grid this season. The British side lead the constructors' standings, with Verstappen's Red Bull team trailing in third.
"I probably wasn't outright ready to go up against Red Bull and Max," added Norris, 25, now in his sixth season on the Formula One grid. I think I am now, but it is probably too late. No-one has gone up against Max so early on in their career and put up a reasonable fight. I am there but nobody else is doing it.
"This was my first opportunity to see where I stand. I was not at the level where I needed to be at the beginning of the year but since the summer break I have done a very good job and I have performed very well."
He continued: "I still need to make tweaks, and I still need to make improvements, but for the first time I am confident to say that I have what is needed to fight for a championship.
"That doesn't mean I am complete or perfect and if you want to beat Max you have to be close to perfect - he is one of the best the sport will ever see - but the main thing I can take away from this season is that I have what it takes to fight for a world championship."
