Ferrari dominated Friday practice at the French Grand Prix, suggesting the former champions may be back on form after losing ground to McLaren.
Brazilian Felipe Massa set the fastest time in the second session with a lap of one minute 15.453 seconds, with team-mate Kimi Raikkonen just behind.
The positions were reversed in the morning session, when Finn Raikkonen was fastest in 1:15.382.
The Ferraris were well clear of the McLaren drivers throughout the day.
World championship leader Lewis Hamilton was the faster of the two silver cars in the afternoon, setting the fourth fastest time.
He was 0.327secs adrift of Massa and just behind the Toro Rosso of American Scott Speed.
"We will be stronger over the weekend than we appear today and so I am not too worried about the results so far"
But the world champion had been third fastest behing the Ferraris in the morning session, when Hamilton was only sixth, 0.123secs behind.
Alonso said the times did not reflect McLaren's potential for the race.
"We could have been faster today," he said, "and there is still a little bit of work to do tomorrow on the set-up.
"However I think we will be stronger over the weekend than we appear today and so I am not too worried about the results so far."
Hamilton leads the world championship by 10 points from Alonso heading into Sunday's race, with Massa a further nine points adrift.
Hamilton suffered his first technical failure this season in the morning session.
The 22-year-old pulled off at the Adelaide hairpin before completing a timed lap when the engine protection system kicked in as the Mercedes unit was running too cool.
The two McLarens were split by the Williams of Nico Rosberg and David Coulthard's Red Bull in the morning.
In the afternoon, there were three cars between them.
Vitantanio Liuzzi made it two Toro Rossos in the top five, with Coulthard and Rosberg again showing impressive speed.
606: DEBATE
Anthony Davidson's Super Aguri and Ralf Schumacher's Toyota completed the afternoon top 10.
Jenson Button continued to struggle for Honda. The Englishman was 14th in the morning and 15th in the afternoon.
Times from Friday's first practice at French Grand Prix at Magny-Cours:
1. Kimi Raikkonen (Fin) Ferrari 1:15.382
2. Felipe Massa (Brz) Ferrari 1:15.447
3. Fernando Alonso (Spa) McLaren-Mercedes 1:16.154
4. Nico Rosberg (Ger) Williams-Toyota 1:16.214
5. David Coulthard (GB) Red Bull-Renault 1:16.268
6. Lewis Hamilton (GB) McLaren-Mercedes 1:16.277
7. Nick Heidfeld (Ger) BMW Sauber 1:16.338
8. Alexander Wurz (Aut) Williams-Toyota 1:16.407
9. Robert Kubica (Poland) BMW Sauber 1:16.441
10. Jarno Trulli (Ita) Toyota 1:16.603
11. Vitantonio Liuzzi (Ita) Toro Rosso-Ferrari 1:16.895
12. Takuma Sato (Jpn) Super Aguri-Honda 1:16.967
13. Rubens Barrichello (Brz) Honda 1:16.990
14. Jenson Button (GB) Honda 1:17.047
15. Scott Speed (US) Toro Rosso-Ferrari 1:17.103
16. Anthony Davidson (GB) Super Aguri-Honda 1:17.166
17. Ralf Schumacher (Ger) Toyota 1:17.168
18. Giancarlo Fisichella (Ita) Renault 1:17.226
19. Heikki Kovalainen (Fin) Renault 1:17.348
20. Mark Webber (Aus) Red Bull-Renault 1:17.435
21. Christijan Albers (Ned) Spyker-Ferrari 1:18.178
22. Adrian Sutil (Ger) Spyker- Ferrari 1:18.419
Times from second session:
1. Massa 1:15.453
2. Raikkonen 1:15.488
3. Speed 1:15.773
4. Hamilton 1:15.780
5. Liuzzi 1:15.952
6. Coulthard 1:15.958
7. Rosberg 1:16.003
8. Alonso 1:16.049
9. Davidson 1:16.162
10. Schumacher 1:16.184
11. Fisichella 1:16.205
12. Kubica 1:16.236
13. Wurz 1:16.260
14. Trulli 1:16.285
15. Button 1:16.395
16. Webber 1:16.562
17. Kovalainen 1:16.735
18. Barrichello 1:16.950
19. Heidfeld 1:16.968
20. Sato 1:17.165
21. Sutil 1:18.213
22. Albers 1:18.708
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