Nico Rosberg led team-mate Lewis Hamilton in a Mercedes one-two in opening Chinese Grand Prix practice, as the squad returned to the scene of its first modern-era Formula 1 victory one year ago.
Warring Red Bull duo Mark Webber and Sebastian Vettel were next up, but a second off the Mercedes' pace.
Mercedes took charge on the last lighter-fuel runs going into the final half-hour of the session.
Rosberg initially put in a 1m37.872s to knock Felipe Massa's Ferrari off the top spot.
This mark was then pipped by Webber, who went 0.2s faster just a minute later.
But Rosberg had more speed to come. Despite signs of tyre graining and being eight laps into a stint, he unleashed a 1m36.904s, backed off for a lap, then delivered the best lap of the morning with a 1m36.717s.
Mercedes then appeared to have superior pace on the race stint simulations in the final half-hour, although fuel load variations inevitably skew this picture.
Hamilton was ultimately 0.454s down on his team-mate, but 0.487s clear of Webber. Three tenths of a second split the two Red Bulls in third and fourth.
Jenson Button had been among the first to set a flying lap, albeit over half an hour into the session, and kept his McLaren near the top for a long while.
He ended up sixth, between the Ferraris of Fernando Alonso and Massa.
Button's team-mate Sergio Perez provided a bizarre end to the session when he crashed in the pitlane entry gravel trap, replicating the infamous incident that ended McLaren predecessor Hamilton's 2007 Chinese GP.
Adrian Sutil also had a stint in first place before ending up eighth, two places in front of Force India team-mate Adrian Sutil. Romain Grosjean's Lotus split them.
The Frenchman's team-mate Kimi Raikkonen provided the session's other main incident when he ran wide at Turn 9 and spun back across the track. Raikkonen resumed without damage.
Sauber rookie Esteban Gutierrez also had an excursion, exploring the gravel at Turn 1.
Ex-HRT third driver Ma Qing Hua made his Caterham debut in Charles Pic's car at his home event. The GP2 racer was last, 1.5s off team-mate Giedo van der Garde.
Pos Driver Team/Car Time Gap Laps
1. Nico Rosberg Mercedes 1m36.717s 21
2. Lewis Hamilton Mercedes 1m37.171s + 0.454s 20
3. Mark Webber Red Bull-Renault 1m37.658s + 0.941s 21
4. Sebastian Vettel Red Bull-Renault 1m37.942s + 1.225s 20
5. Fernando Alonso Ferrari 1m37.965s + 1.248s 17
6. Jenson Button McLaren-Mercedes 1m38.069s + 1.352s 24
7. Felipe Massa Ferrari 1m38.095s + 1.378s 14
8. Adrian Sutil Force India-Mercedes 1m38.125s + 1.408s 21
9. Romain Grosjean Lotus-Renault 1m38.398s + 1.681s 17
10. Paul di Resta Force India-Mercedes 1m38.561s + 1.844s 15
11. Kimi Raikkonen Lotus-Renault 1m38.790s + 2.073s 16
12. Jean-Eric Vergne Toro Rosso-Ferrari 1m39.057s + 2.340s 19
13. Pastor Maldonado Williams-Renault 1m39.158s + 2.441s 22
14. Nico Hulkenberg Sauber-Ferrari 1m39.180s + 2.463s 21
15. Daniel Ricciardo Toro Rosso-Ferrari 1m39.336s + 2.619s 19
16. Sergio Perez McLaren-Mercedes 1m39.360s + 2.643s 20
17. Valtteri Bottas Williams-Renault 1m39.392s + 2.675s 20
18. Esteban Gutierrez Sauber-Ferrari 1m40.032s + 3.315s 22
19. Jules Bianchi Marussia-Cosworth 1m41.966s + 5.249s 16
20. Max Chilton Marussia-Cosworth 1m42.056s + 5.339s 18
21. Giedo van der Garde Caterham-Renault 1m42.083s + 5.366s 21
22. Ma Qing Hua Caterham-Renault 1m43.545s + 6.828s 20