McLaren finished well clear at the top of the timesheet in the second free practice session at Melbourne, as Lewis Hamilton and Jenson Button made the best of the little dry running available.
A light drizzle began just five minutes before the session and turned to proper rain as the cars headed out for their installation laps.
Twenty minutes of quiet followed until the rain eased and the cars headed back out for what would only be a 15-minute window of dry track time.
Nico Rosberg was first up to speed, at a similar pace to the day's earlier session, before McLaren team-mates Jenson Button and Lewis Hamilton squabbled over the top spot.
Button was first to knock Rosberg off but Hamilton followed just a few seconds behind and bettered his time. Button then set a 1m26.0s next time round, which was again beaten by Hamilton, who did a 1m25.8s.
The rain returned before the battle could go any further, driving the cars back in. Jaime Alguersuari was the only one to stay out, but he had a big moment exiting the final corner and also surrendered to the pits.
There were less than 10 minutes remaining by the time the track was dry enough for any more competitive laptimes, and Mark Webber and Michael Schumacher jumped up to third and fourth fastest with late efforts.
Sebastian Vettel was also set for a late improvement but spun approaching Turn 6 when he dropped his left-side tyres onto the grass under braking. He finished the session 16th.
Vitaly Petrov, Sebastien Buemi, Adrian Sutil, Vitantonio Liuzzi, Rubens Barrichello and Nico Rosberg completed the top 10, all with times set during the first dry spell.
The Ferraris missed the best window of dry running so ended just 15th, for Fernando Alonso, and 17th, Felipe Massa, on the timesheet.
It was another difficult session for the newcomers. Timo Glock sat out almost all of it while his gearbox oil leak from the day's earlier session was repaired. The German only appeared for nine laps at the end. Lucas di Grassi didn't emerge after his installation laps, due to an issue with his telemetry box.
At HRT, Karun Chandhok had to park his car 200 yards into his out lap when he lost drive with a suspected gearbox failure, while Bruno Senna missed the whole session after his car developed a fuel pressure problem.
Lotus fared better, with Heikki Kovalainen and Jarno Trulli completing plenty of laps and Kovalainen finishing the session 18th, quicker than Alguersuari's Toro Rosso. Trulli was 20th, but complained of a glitch in his engine hindering its driveability.
Pos Driver Team Time Laps
1. Hamilton McLaren-Mercedes 1:25.801 13
2. Button McLaren-Mercedes 1:26.076 + 0.275 16
3. Webber Red Bull-Renault 1:26.248 + 0.447 22
4. Schumacher Mercedes 1:26.511 + 0.710 16
5. Petrov Renault 1:26.732 + 0.931 26
6. Buemi Toro Rosso-Ferrari 1:26.832 + 1.031 29
7. Sutil Force India-Mercedes 1:26.834 + 1.033 22
8. Liuzzi Force India-Mercedes 1:26.835 + 1.034 17
9. Barrichello Williams-Cosworth 1:26.904 + 1.103 25
10. Rosberg Mercedes 1:26.956 + 1.155 22
11. Kubica Renault 1:27.108 + 1.307 28
12. de la Rosa Sauber-Ferrari 1:27.108 + 1.307 25
13. Kobayashi Sauber-Ferrari 1:27.455 + 1.654 23
14. Hulkenberg Williams-Cosworth 1:27.545 + 1.744 25
15. Alonso Ferrari 1:29.025 + 3.224 20
16. Vettel Red Bull-Renault 1:29.134 + 3.333 19
17. Massa Ferrari 1:29.591 + 3.790 21
18. Kovalainen Lotus-Cosworth 1:29.860 + 4.059 15
19. Alguersuari Toro Rosso-Ferrari 1:30.510 + 4.709 43
20. Trulli Lotus-Cosworth 1:30.695 + 4.894 17
21. Glock Virgin-Cosworth 1:32.117 + 6.316 9
22. di Grassi Virgin-Cosworth 2
23. Chandhok HRT-Cosworth 1
24. Senna HRT-Cosworth
All Timing Unofficial