Williams' Nico Rosberg dominated Formula One's first day of practice at the Australian Grand Prix on Friday while McLaren's world champion Lewis Hamilton languished near the bottom of the timesheets.
Germany's Rosberg, son of Finland's 1982 champion Keke, lapped quickest in both of the afternoon sessions at a sunny Albert Park while Hamilton was 18th of the 20 drivers in the second.
Only Renault's Brazilian Nelson Piquet and 20-year-old Swiss rookie Sebastien Buemi in the Toro Rosso were slower.
The three teams using controversial rear diffusers -- Brawn GP, Toyota and Williams -- showed why their rivals were so concerned by filling six of the top seven places in a second session held late in the afternoon.
The trio had been subjected to protests by other teams, who argued that their cars broke the rules, on Thursday before stewards cleared them for Sunday's race with an appeal now pending.
Rosberg, who finished third in the Melbourne season-opener last year, led Japanese team mate Kazuki Nakajima in a Williams one-two in the first practice.
His best time of one minute 26.053 in the second was 0.104 quicker than Brazilian Rubens Barrichello in the Brawn and well inside the 2008 pole of 1:26.714 set by last year's race winner Hamilton.
Hamilton, who has already warned that it would be tough to score a point this weekend in an uncompetitive car struggling for pace, showed that McLaren's problems were far from imaginary.
His Finnish team mate Heikki Kovalainen reinforced that impression by finishing just one place ahead of the 24-year-old at the end of the day.
Hamilton was also the slowest of those with Mercedes engines, with Force India's Adrian Sutil a strong ninth in both sessions.
Jenson Button, an early favourite after Mercedes-powered Brawn set the pace in testing after emerging from the remains of departed Honda, was sixth and fifth respectively.
Germany's Sebastian Vettel, preparing for his Red Bull debut after moving up from sister team Toro Rosso, completed just four laps in the first session and then spun off and stalled in the second.
His Australian team mate Mark Webber did only seven laps in first practice but turned in the fourth fastest time in the later session.
Champions Ferrari had a largely anonymous day.
Kimi Raikkonen, the 2007 champion, was 11th in the final session while Brazilian team mate Felipe Massa was one place ahead.
The regulations have changed dramatically this year, with cars running on slick tyres and with new-look aerodynamics. Some teams are also using the new KERS energy recovery systems that give drivers an extra boost at the push of a button.
Sunday's race is also starting later than usual to cater for European television audiences, with the finish expected in the evening twilight.