Sebastian Vettel says he recognised the potential in 2017 title rival Lewis Hamilton the first time their paths crossed as youngsters in karting.

Despite winning seven of the last nine world championships between them, this year is the first time Vettel and Hamilton have properly faced off for a title. The pair are easily the most successful drivers of the modern era and have enjoyed dominant spells either side of the current V6 turbo era.

Both men were highly rated when coming through the junior categories but took different routes into F1 -- Hamilton won the 2006 GP2 feeder series before stepping up to McLaren, while Vettel was leading the 2007 Formula Renault 3.5 championship when he stepped up to F1 with BMW and Toro Rosso for the second half of that season. They had crossed paths before F1 -- notably in the 2005 Formula 3 championship won by Hamilton.

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In an interview with former Red Bull teammate and rival Mark Webber on Channel 4, Vettel was asked when he first thought Hamilton would reach the top of F1, saying: "I remember him in 1999, he finished third in the European Championship in karting. And the team I was racing with was saying 'this guy, he will go all the way'.

"On-on-one was more Formula 3, I was in my first year, he was in the second year and blowing everyone away. I didn't get much chance, I joined him on the podium a couple of times.

"That was when you saw no matter what -- yes, [you can say] great year, second year so more experience, great car, whatever -- but whatever the conditions, he was always there and delivering. In the end when someone is always there, always delivering -- you might get lucky for a day, or whatever, but not for a year."

Lewis Hamilton was a year ahead of Sebastian Vettel when he won the 2005 Formula 3 championship. Sutton Images

Vettel leads the Mercedes driver by 14 points at the summer break, with nine races to follow in the second half of the season, and is convinced he can still be ahead when the chequered flags drops in Abu Dhabi in late November.

"He's extremely quick, extremely gifted at what he does. I don't think it's a huge challenge for him to drive quickly or to adapt with different conditions and so on. He's always there. But he's not unbeatable."