Gronholm is competing in his 18th Rally of Finland

The Ford driver made a good start to the day, winning three of the first four special stages in wet conditions.

Although Loeb made a move in the afternoon when it dried up, Gronholm managed to stay ahead of the Frenchman.

Mikko Hirvonen, another Finn and Gronholm's Ford Focus team-mate, lies in third place 43.5 seconds back.

Gronholm trails Loeb by 33 points in the overall standings but has dominated the Finnish event in recent years, winning in five of the last six years, while Loeb is chasing his first win in the event.

"My times on the first few stages were very good, but the other drivers woke up a bit," said Gronholm.

"In the afternoon I was too cautious, especially on the jumps. I need to take a few more risks."

Petter Solberg, the 2003 world champion from Norway, was fourth, 52.9 behind, in a Subaru.

Solberg did not finish last week's rally in Germany and is only sixth in the overall standings.

Day One Classification
1. Marcus Gronholm (Fin) Ford 1:12:59.600
2. Sebastien Loeb (Fra) Citroen +00:12.000
3. Mikko Hirvonen (Fin) Ford 00:43.500
4. Petter Solberg (Nor) Subaru 00:52.900
5. Henning Solberg (Nor) Peugeot 01:47.200
6. Chris Atkinson (Aus) Subaru 02:17.100
7. Daniel Sordo (Sp) Citroen 02:45.000
8. Gianluigi Galli (Ita) Peugeot 02:49.600
9. Jussi Valimaeki (Fin) Mitsubishi 03:02.300
10. Janne Tuohino (Fin) Citroen 03:06.000