Sebastian Vettel dominates practice at Ferrari . F1 championship leader fastest in one minute 38.125 seconds sessions . Sebastian Vettel star can clinch third straight world title this weekend . Nearest challenger Fernando Alonso second fastest for Ferrari in third runs .
Sebastian Vettel dominates practice at United States Grand Prix . F1 championship leader fastest in both morning and afternoon sessions . Red Bull star can clinch third straight world title this weekend . Nearest challenger Fernando Alonso third fastest for Ferrari in second runs .