Sir Jackie Stewart may not agree, but defending drivers champion Sebastian Vettel will stand at the threshold of greatness when he lines up for his 100th Formula One race in Austin on Sunday week.

The 25-year-old German can clinch his third successive title with Red Bull and become the youngest triple champion in F1 history if he wins the United States Grand Prix.

And, after his near-amazing drive from a pit lane start to finish on the podium at last Sunday's Abu Dhabi Grand Prix, there are few observers left who have any reservations about Vettel's status in the hall of champions.

Stewart may have commented recently that he was yet to be convinced that Vettel has become a great driver. But others have already declared that the 'baby faced assassin' is one of the greatest.

Certainly, his Red Bull team are - as expected - full of admiration not only the technical merit of the champion, who heads across the Atlantic with a 10-points advantage ahead of his only remaining rival, Fernando Alonso of Ferrari.

Vettel's team are also in awe of the German's mental strength.

Team chief Christian Horner revealed earlier this week that Vettel was the only man in the team convinced he could pull off a good result.

"Fernando (Alonso) looked very revved up on the podium having gone forward four places, while Seb had gone to the podium via losing his front wing," said Horner.

"Seb is going about his job the way he does it. Mentally he is very strong. Before the race I went to see him to wish him good luck, and he is in there playing a drum kit with his trainer.

"He said, 'I will see you later on the podium'.

"He was the one guy in the briefing room on Saturday night - while the rest of us were ready to slit our wrists - who said he could do it.

"It is that mental strength that he has that is one of his biggest assets."

All of this means that the American event will present Vettel with his first authentic opportunity to confirm he has kept his crown -- but Horner said that will make no difference to the way that the Red Bull team approach the race weekend.

"As we have seen before, as we did last weekend, when you are on the edge things can go wrong," he said.

"And we cannot take anything for granted. We have to go to Austin to attack the weekend. It is a new track for everybody and we have to go there and get a good result."

Vettel has conceded that he is amazed at how quickly he has clocked up his 99 races to date.
Before last Sunday's race, he said: "Well, 98 times so far when the lights went off, all 98 times I've been through the first corner - you don't realise how quickly time goes by.

"If you look back to the year I started F1, in 2007, it doesn't feel like that long ago.

"It's two years ago that we won the first championship and there have been so many races that have happened. When I wake up in the morning, all I think about is now. I'm not thinking about two years ago.

"I think I have learned a lot. It's the same for the team. It made us all tougher. The spirit hasn't changed. We're still hungry, but winning the title has been an important goal - the most important thing I wanted to achieve in my life."