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.
In the second practice, it was Felipe Massa who put Ferrari on top as Rosberg had to settle for fourth this time, while Kimi Raikkonen and Fernando Alonso took second and third places.
Initially Rosberg and Mercedes resumed their commanding morning form by setting the initial pace, while team-mate Lewis Hamilton was next up.
The soft tyre runs started early, with Mark Webber switching from the medium rubber just 20 minutes in.
He used his new Pirellis to outpace Rosberg by 0.6s and claim first place, although the German soon retaliated with his own soft-tyre dash and got back in front.
But the second half of the afternoon was all about Ferrari and Massa.
A 1m35.340s from Massa on the soft tyres put him in front, and that was where he stayed.
More impressively, he maintained his speed better than most on his subsequent long run with medium tyres, on a day when radio complaints about graining were perhaps even more prevalent than usual.
Rosberg was eventually pushed down to fourth place as Raikkonen emerged as Massa's closest rival, getting within 0.152s.
Fernando Alonso increased Ferrari's satisfaction with third place, albeit 0.4s off his team-mate.
Rosberg and Webber completed the top five, while Jenson Button showed encouraging form for McLaren again in sixth, ahead of Hamilton.
2013 Chinese GP Free Practice 1 classification
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
2013 Chinese GP Free Practice 2 classification
Pos Driver Team Time Gap Laps
1. Felipe Massa Ferrari 1m35.340s 32
2. Kimi Raikkonen Lotus-Renault 1m35.492s + 0.152s 32
3. Fernando Alonso Ferrari 1m35.755s + 0.415s 30
4. Nico Rosberg Mercedes 1m35.819s + 0.479s 35
5. Mark Webber Red Bull-Renault 1m36.092s + 0.752s 31
6. Jenson Button McLaren-Mercedes 1m36.432s + 1.092s 29
7. Lewis Hamilton Mercedes 1m36.496s + 1.156s 39
8. Adrian Sutil Force India-Mercedes 1m36.514s + 1.174s 32
9. Paul di Resta Force India-Mercedes 1m36.595s + 1.255s 33
10. Sebastian Vettel Red Bull-Renault 1m36.791s + 1.451s 27
11. Sergio Perez McLaren-Mercedes 1m36.940s + 1.600s 16
12. Romain Grosjean Lotus-Renault 1m36.963s + 1.623s 31
13. Esteban Gutierrez Sauber-Ferrari 1m37.103s + 1.763s 22
14. Daniel Ricciardo Toro Rosso-Ferrari 1m37.206s + 1.866s 39
15. Jean-Eric Vergne Toro Rosso-Ferrari 1m38.127s + 2.787s 34
16. Valtteri Bottas Williams-Renault 1m38.185s + 2.845s 18
17. Nico Hulkenberg Sauber-Ferrari 1m38.211s + 2.871s 32
18. Pastor Maldonado Williams-Renault 1m38.276s + 2.936s 34
19. Jules Bianchi Marussia-Cosworth 1m38.725s + 3.385s 29
20. Giedo van der Garde Caterham-Renault 1m39.271s + 3.931s 21
21. Charles Pic Caterham-Renault 1m39.814s + 4.474s 27
22. Max Chilton Marussia-Cosworth 1m43.227s + 7.887s 5