Felipe Massa led a commanding Ferrari one-two in the second practice session in Melbourne.
Apart from a brief interruption by Alonso, Massa held sway throughout the session. He opened with a 1:29.393 lap, then found another 0.8 seconds next time through.
When Alonso closed to within 0.009 seconds on his second run, Massa improved to a 1:28.111 to increase the gap to four tenths.
The McLaren nipped ahead by 0.071 seconds after half an hour, shortly before 15 minutes of the session were lost to a red flag.
Rubens Barrichello was the primary cause, spinning lightly into the barriers after tagging the grass with his Honda's left rear wheel approaching the final corners.
At the same time, Heikki Kovalainen's Renault ground to a halt at Turn 3, ending a difficult session in which he had been a second off teammate Giancarlo Fisichella after their first flying laps, and then took to the grass at Turn 1 on his next run.
Ominously for Renault, who had enjoyed promising reliability in the winter, Fisichella also stopped on track in the closing minutes of the session.
When practice resumed, Massa quickly usurped Alonso and continued to improve his time on successive laps until reaching the 1:27.353 that would stand as the afternoon benchmark with nine minutes left.
Shortly afterwards teammate Kimi Raikkonen, who had so far had a low-key session, jumped to second, pushing the continually impressive Lewis Hamilton back to third. The GP2 champion ended up 0.2 seconds quicker than teammate Alonso, who eventually dropped back to sixth.
The world champion was shuffled down the order as Fisichella improved to fourth before pulling off, Nick Heidfeld again demonstrated BMW's pace by taking fifth, and Alex Wurz made a surprise late leap to sixth for Williams, who also had Nico Rosberg in eighth place.
Robert Kubica and David Coulthard - who had twice visited the Turn 1 gravel - completed the top ten.
With the teams eager to make the most of the dry track after this morning's rain, the opening minutes of the second session had seen a flurry of activity and incident, with almost the entire field immediately embarking on flying laps - and several drivers heading straight off the track.
Within the first five minutes of running, Nick Heidfeld had followed Jarno Trulli into a synchronised trip across the Turn 1 gravel, Vitantonio Liuzzi had spun, and both Robert Kubica and Nico Rosberg had gone off at Turn 12, with the BMW spinning and the Williams gathering up a wild moment. Kubica and Liuzzi would briefly revisit the gravel later in the session.
The teams are the centre of the looming 'customer car' controversy produced very different performances.
While the Toro Rossos barely featured in the top 20 all afternoon, Super Aguri's Anthony Davidson and Takuma Sato outpaced the works Hondas. Although Davidson was ultimately the quicker of the pair in 11th, Sato had held ninth in the middle stages of the session.
Pos Driver Team Time Laps
1. Massa Ferrari (B) 1:27.353 32
2. Raikkonen Ferrari (B) 1:27.750 + 0.397 33
3. Hamilton McLaren-Mercedes (B) 1:27.829 + 0.476 29
4. Fisichella Renault (B) 1:27.941 + 0.588 33
5. Heidfeld BMW Sauber (B) 1:27.970 + 0.617 27
6. Wurz Williams-Toyota (B) 1:27.981 + 0.628 31
7. Alonso McLaren-Mercedes (B) 1:28.040 + 0.687 25
8. Rosberg Williams-Toyota (B) 1:28.055 + 0.702 29
9. Kubica BMW Sauber (B) 1:28.281 + 0.928 26
10. Coulthard Red Bull-Renault (B) 1:28.495 + 1.142 23
11. Davidson Super Aguri-Honda (B) 1:28.727 + 1.374 28
12. Trulli Toyota (B) 1:28.921 + 1.568 33
13. Sato Super Aguri-Honda (B) 1:29.009 + 1.656 23
14. Button Honda (B) 1:29.066 + 1.713 30
15. Barrichello Honda (B) 1:29.542 + 2.189 12
16. R.Schumacher Toyota (B) 1:29.574 + 2.221 26
17. Webber Red Bull-Renault (B) 1:29.801 + 2.448 11
18. Kovalainen Renault (B) 1:30.097 + 2.744 10
19. Speed Toro Rosso-Ferrari (B) 1:30.383 + 3.030 28
20. Sutil Spyker-Ferrari (B) 1:31.108 + 3.755 35
21. Albers Spyker-Ferrari (B) 1:31.175 + 3.822 32
22. Liuzzi Toro Rosso-Ferrari (B) 1:31.693 + 4.340 16
All timing unofficial
The Stig