Mercedes driver Lewis Hamilton produced a sensational performance to set the pace in first practice at the Singapore Grand Prix.
Hamilton headed Red Bull's Mark Webber by 0.365 seconds, with the Australian's team-mate Sebastian Vettel third.
The second Mercedes of Nico Rosberg was fourth, 1.184secs behind his team-mate.
Lotus drivers Kimi Raikkonen and Romain Grosjean were fifth and sixth ahead of Vettel's title rival Ferrari's Fernando Alonso, who was 1.3secs off the pace.
Alonso is 53 points behind Vettel heading into this race, with 175 still available in the remaining seven grands prix and really needs to beat the German to revive his dwindling hopes.
But the Ferrari appeared to be struggling for grip as the team experimented with upgrades, including new front and rear wings, and diffuser.
Alonso had a couple of near-misses with the wall and at one point had a moment at Turn 13 when he had a wobble during braking and ran wide on entry.
The rear of the car looked loose when Alonso pushed hard and the team will need to make some changes if they are to compete at the front this weekend.
His team-mate Felipe Massa, who will be replaced by Raikkonen next season, was 12th, 1.1secs behind Alonso.
McLaren's Sergio Perez was eighth fastest after learning ahead of the session that his drive is under threat for next season.
His team are trying to prise Alonso away from Ferrari to team him with Button. Perez was told of the development no more than an hour before first practice started.
Perez was 0.3secs and six places ahead of Button, who was down in 14th, behind Toro Rosso's Jean-Eric Vergne, Sauber's Esteban Gutierrez, Williams's Pastor Maldonado, Massa and the second Williams of Valtteri Bottas.
The session suggested that Mercedes and Red Bull are clear at the front of the field - particularly Hamilton and the Red Bulls.
The Mercedes did not look as good as the Red Bull out on the track, but Hamilton was at his acrobatic best as he danced the car around the tight corners of the demanding 3.18-mile Marina Bay street track.
Hamilton finished the session 0.830secs clear of Vettel, who inherited victory in Singapore last year when the Englishman suffered a gearbox failure in his McLaren while leading the race.
BBC 5 live analyst and Williams development driver Susie Wolff said: "I think the battle is going to be between Mercedes and Red Bull. Lotus are going to have to do a bit of work to catch up.
BBC F1 technical analyst Gary Anderson added: "I think Ferrari will join that club after they worked out the best combination of the jigsaw of bits they were trying in this session."