Sebastian Vettel dominates practice at United States Grand Prix . F1 championship leader fastest in both morning and afternoon sessions . Earlier , Vettel was quickest in the first competitive F1 action on the 5.516km track with a time of one minute 38.125 seconds . Red Bull star to clinch third straight world title this weekend . Nearest challenger Fernando Alonso third fastest for Ferrari in second session .
Sebastian Vettel dominates practice at United States Grand Prix . F1 championship leader fastest in both morning and afternoon sessions . Red Bull star to clinch third straight world title this weekend . Nearest challenger Fernando Alonso third fastest for Ferrari in second session .