Nico Rosberg led both practice sessions Friday in his Williams Toyota car

Officially bearing the 'number 1' for the first time, Lewis Hamilton never rose higher than sixteenth quickest as McLaren's worst fears about its performance were apparently realized on Friday.

With the uncertainty of winter testing now behind, the Briton outpaced only the struggling Nelson Piquet - watched on by his famous triple world championship-winning father - and Swiss rookie Sebastien Buemi, as the three hours of practice wound down Albert Park.

The reigning world champion was also slower than his teammate Heikki Kovalainen throughout Friday.

The shadows of the early evening grew longer as Melbourne prepared for its 'twilight race' debut, leaving observers wondering if Williams has returned to top form, after Nico Rosberg headed the times in both 90 minute sessions.

Even Nakajima was fast in his Williams Toyota car

His teammate Kazuki Nakajima was also quick, but so too were the other runners (Brawn and Toyota) who are accused of using dubious rear diffusers.

Brawn were the pre-Friday favorites here, and Rubens Barrichello in the late session posted the second fastest time of the entire day.  Jenson Button's best times fell a couple of tenths shy.

Barrichello, extending his record as the most experienced veteran in the sport's history, insists the Mercedes-powered car is not only being boosted by a clever rear end.

"If you would take it (the diffuser) out completely, we would lose some time but not everything.  The car is competitive for a whole bunch of reasons," he said.

Apparently struggling are expected title protagonists BMW-Sauber, whose drivers were never inside the top ten, and Ferrari, a second off the leading pace in the ultimate session after a more promising start.

Sebastian Vettel, meanwhile, had a disastrous day, stranded out on the circuit twice: first with an hydraulic problem, and finally when he spun into the gravel after putting a tire on the grass verge.

Practice 2 results

Pos	Driver	Team	Time	Behind	Laps
1.	Rosberg	Williams-Toyota	1:26.053	+0.000	36
2.	Barrichello	Brawn-Mercedes	1:26.157	+ 0.104	38
3.	Trulli	Toyota	1:26.350	+ 0.297	42
4.	Webber	Red Bull-Renault	1:26.370	+ 0.317	30
5.	Button	Brawn-Mercedes	1:26.374	+ 0.321	38
6.	Glock	Toyota	1:26.443	+ 0.390	42
7.	Nakajima	Williams-Toyota	1:26.560	+ 0.507	33
8.	Vettel	Red Bull-Renault	1:26.740	+ 0.687	19
9.	Sutil	Force India-Mercedes	1:27.040	+ 0.987	29
10.	Massa	Ferrari	1:27.064	+ 1.011	35
11.	Raikkonen	Ferrari	1:27.204	+ 1.151	32
12.	Alonso	Renault	1:27.232	+ 1.179	28
13.	Fisichella	Force India-Mercedes	1:27.282	+ 1.229	32
14.	Heidfeld	BMW-Sauber	1:27.317	+ 1.264	34
15.	Kubica	BMW-Sauber	1:27.398	+ 1.345	36
16.	Bourdais	Toro Rosso-Ferrari	1:27.479	+ 1.426	36
17.	Kovalainen	McLaren-Mercedes	1:27.802	+ 1.749	35
18.	Hamilton	McLaren-Mercedes	1:27.813	+ 1.760	31
19.	Piquet	Renault	1:27.828	+ 1.775	35
20.	Buemi	Toro Rosso-Ferrari	1:28.076	+ 2.023	33