Nico Rosberg set the early pace in opening practice for Sunday's Singapore Grand Prix.
The German, who heads into the night race 53 points adrift of Lewis Hamilton, posted a best lap of one minute and 47.955 seconds to lead the field.
Hamilton was next up in the sister Mercedes, albeit 0.319secs adrift of Rosberg's quickest lap at the challenging Marina Bay Street Circuit.
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Red Bull, who have endured a lacklustre campaign so far, were hopeful the slow-speed nature of this street circuit would suit their package.
Daniel Ricciardo ended the session in third, fractionally slower than Hamilton. Ferrari's Sebastian Vettel, a three-time winner in Singapore, was fourth despite a spin at turn four in the closing stages.
The opening practice session started at dusk, but ended under the lights in the seventh edition of Formula One's only night race. Air temperature approached 30 degrees with a humidity of 73 per cent.
Hamilton arrived in the Far East only one victory shy of his idol Ayrton Senna's tally of 41 career wins. But Rosberg, who was using Mercedes' new-specification engine after his failed at the last race, was the early pacesetter.
McLaren, like Red Bull, are also hopeful the low-speed circuit will suit their cars.
Fernando Alonso ended the session in 11th place, a little over two seconds shy of Rosberg, with team-mate Jenson Button in 15th, three-tenths slower than his team-mate.
The 90-minute session ended prematurely after Alexander Rossi, on his Grand Prix debut, slammed his Manor into the barriers.
Rossi, who is replacing Roberto Merhi at five of the remaining seven races, clambered out of his cockpit after crashing at turn 18 with five minutes remaining .
The American sustained significant damage to the right-hand side of his Manor and his mechanics will now face a race against time to get his car in a fit condition to compete in the second practice session which gets under way at 2130 local time (2.30pm BST).
Kimi Raikkonen was fifth for Ferrari with Williams driver Valtteri Bottas in sixth. Toro Rosso's Max Verstappen finished seventh, the Force India of Nico Hulkenberg was eighth, Carlos Sainz, in the other Toro Rosso, ninth with the Lotus driver of Pastor Maldonado completing the top 10.