Nico Rosberg made a much-needed strong start to the Singapore GP weekend as he set the pace from title leader Lewis Hamilton.
Having fallen the equivalent of two race victories adrift of his Mercedes team-mate after his late engine blow-out at Monza, at the end of a weekend in which Hamilton topped every session, Rosberg struck the first blow at Marina Bay on Friday armed with his brand-new power unit.
Immediately setting the pace at the start of P1, Rosberg was the only man in the session to dip below 1:48, with his quickest lap of 1:47.995 three tenths of a second quicker than that of his team-mate.
The opening session of the Singapore weekend is habitually the least representative of the weekend, given it takes place two hours earlier than Sunday's night race, but Sky F1's practice co-commentator Paul Di Resta said: "Lewis looks like he's struggling in a P1 session more than he has for some time."
Mercedes enjoyed a 1.5s advantage over the field at the half-way point of the session, but their advantage had shrunk to just 0.3s by the chequered flag with Daniel Ricciardo showing promise for Red Bull to take third.
Three-time Singapore victor Sebastian Vettel was fourth for Ferrari, although he was fortunate to not do any serious damage to his car after twice kissing the barriers before just stopping short of the Armco when he ran straight on at Turn Four. Kimi Raikkonen was fifth in the sister Ferrari, ahead of Williams' Valtteri Bottas.
One driver did make significant contact with the barriers, however, and that was Manor new boy Alexander Rossi, who dented what had otherwise been a strong opening session relative to new team-mate Will Stevens by crashing at Turn 18 - the circuit's traditional hot spot.
The American, who only learned he was racing in place of Roberto Merhi on Tuesday, had racked up 18 laps on his first return to F1 machinery since P1 at last season's Belgian GP. Rossi's final time of 1:53.918 was just 0.015s shy of Stevens' benchmark.
Only Manor had been slower than McLaren at high-speed Spa and Monza, but the Woking team's hopes that the slower streets will better suit their underperforming MP4-30 were boosted by the sight of Fernando Alonso finishing just outside the top 10 in 11th place. Team-mate Jenson Button, who had early issues with his car-to-pit radio, was 15th.
Times:
1. N Rosberg, Mercedes, 1:47.995
2. L Hamilton, Mercedes, 1:48.314
3. D Ricciardo, Red Bull, 1:48.331
4. S Vettel, Ferrari, 1:48.494
5. K Raikkonen, Ferrari, 1:48.785
6. V Bottas, Williams, 1:49.380
7. M Verstappen, Toro Rosso, 1:49.466
8. N Hulkenberg, Force India, 1:49.854
9. C Sainz, Toro Rosso, 1:50.019
10. P Maldonado, Lotus, 1:50.068
11. F Alonso, McLaren, 1:50.123
12. S Perez, Force India, 1:50.125
13. F Nasr, Sauber, 1:50.158
14. R Grosjean, Lotus, 1:50.341
15. J Button, McLaren, 1:50.455
16. M Ericsson, Sauber, 1:50.883
17. F Massa, Williams, 1:51.035
18. D Kvyat, Red Bull, 1:51.188
19. W Stevens, Manor, 1:53.903
20. A Rossi, Manor, 1:53.918