Hamilton remains on top in second practice in Austin

Hamilton on the verge of fourth title (1:04)

Jennie Gow reports from Austin ahead of the race that could seal Lewis Hamilton's fourth drivers' championship. (1:04)

AUSTIN -- Lewis Hamilton dominated Friday practice at the U.S. Grand Prix, with the fastest times in both sessions and a 0.4s margin over his nearest rival by the end of the day.

The Mercedes driver could win the championship this weekend if he finishes 16 points clear of Sebastian Vettel on Sunday, and although that seems unlikely -- Vettel would have to finish sixth or lower if Hamilton wins -- Hamilton appears determined to fulfil his side of the equation by securing a sixth win in seven races.

The precise gap to Max Verstappen in second place stood at 0.397s, with half of that (0.198s) coming in the steep run up to Turn 1 and the flowing corners through Turns 3, 4, 5 and 6. But while the Red Bull lacked some pace over one lap, Verstappen's long-run times showed promise and the team from Milton Keynes could once again emerge as a threat for victory on Sunday.

After watching his championship challenge fall apart over the previous three races, Vettel's bad luck spilled over into Friday practice at Austin. He started the second session with a high-speed spin at the penultimate corner before recovering to set the third fastest time -- 0.524s off Hamilton. However, when he returned to the track for his long run he complained that the front end of the car felt "like jelly", prompting a return to the pits where he remained until the closing minutes. The problem limited him to just eight laps over the 90 minute session and resulted in him missing out on crucial race preparation runs.

Valtteri Bottas was fourth fastest in the second Mercedes as he again struggled to match teammate Hamilton over a single lap. By the end of the session the difference between the two Mercedes was 0.611s, with Bottas losing time across all three sectors. Daniel Ricciardo also found himself playing second best to his teammate, with a 0.398s gap to Verstappen in second. However, in his case the deficit was mainly found in the middle sector, suggesting he may have made a mistake on his best attempt on low fuel. To complete the set, Kimi Raikkonen was sixth fastest, 0.322s off Ferrari teammate Vettel, meaning the order of the top six was Mercedes, Red Bull, Ferrari, Mercedes, Red Bull, Ferrari.

The next fastest car was Fernando Alonso's McLaren, nearly 0.8s off Raikkonen's time and 0.156s faster than a group of five cars split by just 0.074s behind him. At the head of that group was Felipe Massa in the Williams ahead of the two Force Indias and two Renaults.

On his debut for Renault, Carlos Sainz held a 0.005s margin over new teammate Nico Hulkenberg thanks to a chunk of time found in the middle sector. Daniil Kvyat was 13th ahead of Kevin Magnussen in the Haas, Stoffel Vandoorne for McLaren and the second Williams of Lance Stroll.

On his F1 debut, Brendon Hartley finished 17th in second practice, 1.226s off Toro Rosso teammate Kvyat. The two Saubers of Pascal Wehrlein and Marcus Ericsson were 18th and 19th ahead of Romain Grosjean, who finished last after complaining of balance issues throughout.