Rosberg fastest as Technical problems strike in Shanghai
Toyota's Timo Glock did only 6 laps due to a gearbox problem, and team mechanics got to work on changing the unit even before the hour-long session had ended.
The unscheduled change will result in a five place grid penalty for the German.
Fernando Alonso gave Glock company at the bottom of the timesheets, after also spending most of the session in the pits.
The Spaniard's Renault was fitted with an interim 'double diffuser' for the first time on Saturday, and it is believed the problem related to the new device.
The two Red Bulls did a combined 15 laps, Christian Horner confirming that Mark Webber and Sebastian Vettel had identical driveshaft problems.
The team boss said the race gearboxes were unaffected.
F1's KERS clan, meanwhile, has continued to dwindle, with only three cars now expected to use the energy recovery technology in Sunday's Chinese grand prix.
Robert Kubica's BMW device was as predicted extracted from his F1.09 overnight, and Renault decided to emulate Fernando Alonso's decision about the technology by also removing it from the sister car driven by Nelson Piquet.
Nico Rosberg headed the third and final practice in Shanghai, after committing the Lewis Hamilton-style mistake of running into the gravel early in the session.
Hamilton was third fastest, behind Jarno Trulli but ahead of Jenson Button's Brawn.