Ferrari's Sebastian Vettel says he is his own "biggest enemy" in his title fight with Lewis Hamilton this year. Vettel, who is 30 points behind the Mercedes driver heading into this weekend's Singapore Grand Prix, has made a number of errors this season. He said: "The biggest enemy is me. If we have something to play with, we have all the chances to do it in our way." Hamilton added that he believed maintaining his advantage over the German was "going to be very tough". Vettel was asked whether he could now not afford to lose any more points, following high-profile errors in the Azerbaijan, French, German and Italian Grands Prix that cost him more than 60 points in total.…