Lewis Hamilton enters the United States Grand Prix this weekend knowing a fourth Formula One world championship is within touching distance.

Four wins from his past five outings - the only blemish a runners-up finish in Malaysia - allied with some misfortune for primary title rival Sebastian Vettel, have propelled Hamilton into a 59-point lead with four races to come.

Victory in Austin, where he has won in each of the past three years, combined with Vettel finishing outside the top five, would see Hamilton claim glory and move alongside the Ferrari man on four world titles.

If Hamilton can only take second, Vettel would need to finish ninth or lower for the Mercedes man to be spraying the champagne come Sunday.

It could be a double celebration for Mercedes, who will secure the constructors' championship if both Hamilton and team-mate Valtteri Bottas claim a podium finish, regardless of placings.

At the opposite end of the field, Toro Rosso's Brendon Hartley looks likely to start his maiden F1 race at the back of the grid due to an accumulation of engine penalties.

But all eyes will be on Hamilton, who could join exalted company in equalling Vettel and Alain Prost's tally of four world championships. Only Juan Manuel Fangio (five) and Michael Schumacher (seven) have more.

WHAT WE LEARNED FROM PRACTICE

Once again, Hamilton looked in complete control during Friday's practice, going quickest in both sessions and setting a new lap record around Circuit of the Americas in FP2 at one minute and 34.668 seconds.

Red Bull's Max Verstappen, who signed a new deal through to 2020 earlier in the day, celebrated by going second quickest, just under four tenths slower than the championship leader.

Vettel spun into the gravel during FP2 but came back out and was third fastest, 0.524secs adrift of Hamilton, and the German seemingly has it all to do to prevent the Mercedes man claiming a fourth straight win in Texas.

Like Verstappen, Fernando Alonso signed a fresh contract this week but it was much the same story in FP1 for the McLaren man as he suffered a hydraulic leak and did not set a time. He did return in FP2 to go seventh quickest.

Carlos Sainz out-paced his new Renault team-mate Nico Hulkenberg in both sessions and there was further bad news for the German after it was announced he would be hit with a 20-place grid penalty for using a fifth engine, turbo and MGU-H.

Alonso's McLaren team-mate Stoffel Vandoorne is set to be pushed back 10 places for using his eighth engine of the season.

STANDINGS

Drivers
1. Lewis Hamilton (Mercedes) – 306
2. Sebastian Vettel (Ferrari) – 247 (-59)
3. Valtteri Bottas (Mercedes) – 234 (-72)
4. Daniel Ricciardo (Red Bull) – 192 (-114)
5. Kimi Raikkonen (Ferrari) – 148 (-158)

Constructors
1. Mercedes – 540
2. Ferrari – 395 (-145)
3. Red Bull – 303 (-237)
4. Force India – 147 (-393)
5. Williams – 66 (-474)

PREVIOUS WINNERS

2016: Lewis Hamilton
2015: Lewis Hamilton
2014: Lewis Hamilton

WEATHER FORECAST

Isolated thunderstorms are predicted for Saturday, which could play havoc with qualifying. Clear skies are forecast for Sunday's race.