Colin Edwards, under pressure to return to his early season form, got his Malaysian Grand Prix weekend off to a perfect start by leading Friday practice at a hot and humid Sepang in Malaysia.

The Tech 3 Yamaha rider - who took two podiums during the first nine rounds of the season, but a best finish of seventh in the seven races since - finished this morning's practice in fourth position, 0.746sec behind 2008 MotoGP world champion Valentino Rossi.

This afternoon's second session looked like it might fail to produce any improvements when thunder signalled the arrival of light rain early in the session, but the moisture cleared soon after the halfway mark.

Aided by the uncertain weather, Honda Gresini's Shinya Nakano sat fastest for much of the afternoon, but lost the top spot to Rossi and then Casey Stoner with one minute remaining, before Edwards sliced 0.303sec under the Australian on his last lap.

Rossi trimmed that margin down to 0.171sec on his final circulation, although the Fiat Yamaha star's best lap of the day remained his 2min 2.693sec morning time - which was just 0.026sec slower than Colin's mark.

Stoner, who can secure second in the world championship this weekend, was third in both sessions, while Nakano concluded the day fourth fastest - doing his hopes of securing the third Kawasaki seat no harm at all.

Rossi's Michelin-shod team-mate Jorge Lorenzo was second fastest this morning, but slipped back to tenth this afternoon - although his morning pace was good enough for fifth on combined times.

Countryman Dani Pedrosa's form went in the opposite direction - the Spaniard, injured at Sepang in pre-season testing, was just 17th this morning but improved to fifth with a fast lap late in this afternoon's session to be the leading Repsol Honda rider.

Loris Capirossi was the top Suzuki rider in both sessions, claiming seventh and sixth places, while Andrea Dovizioso was eighth and then seventh for JiR Team Scot.

Randy de Puniet, fast in pre-season testing at Sepang, was a strong fifth in the morning session, before conceding three places in the afternoon. Nicky Hayden, sixth this morning, and Lorenzo completed the afternoon top ten.

Chris Vermeulen was a consistent eleventh in both sessions, while James Toseland, Marco Melandri, Alex de Angelis and John Hopkins joined Rossi and Lorenzo in lapping slower in the afternoon.

Newly announced 2009 Stiggy Honda WSS rider Anthony West climbed from 15th to twelfth to be the top Kawasaki rider, while Suzuki wild-card Nobuatsu Aoki was 19th and last in both sessions on his hybrid GSV-R.

Friday free practice (2):

1. Edwards
2. Rossi
3. Stoner
4. Nakano
5. Pedrosa
6. Capirossi
7. Dovizioso
8. de Puniet
9. Hayden
10. Lorenzo
11. Vermeulen
12. West
13. Elias
14. Toseland
15. Guintoli
16. de Angelis
17. Melandri
18. Hopkins
19. Aoki