Casey Stoner saved his best for last to snatch the top spot from MotoGP championship leader Jorge Lorenzo at the end of a wet second free practice session at Aragon on Friday.

Dani Pedrosa had been fastest by 0.411sec from Nicky Hayden in the dry morning session - when Lorenzo was third and Stoner fourth - but heavy rain fell just before the start of the afternoon session and the track remained wet throughout.

Despite the total change in conditions, Pedrosa once again led the early stages of the afternoon - and was still leading at the halfway mark of the 45 minute session - but then dropped back to 13th by the chequered flag.

Stoner and Lorenzo were frontrunners throughout, and the pair exchanged the top spot during the final 20 minutes, with the Ducati rider jumping into first place for the final time by 0.568sec from the Fiat Yamaha rider as the chequered flag waved.

Like Lorenzo and Stoner, Hayden was quick in both sessions, finishing third in the wet (+0.7sec) and was just ahead of reigning seven time MotoGP champion Valentino Rossi. As he had been in the dry, Rossi was just over one-second from the top.

Gresini Honda had the top satellite rider in both sessions, with rookie Marco Simoncelli fifth this morning, before team-mate Marco Melandri took over that same position in the afternoon.

Pedrosa's Repsol Honda team-mate Andrea Dovizioso was 8-6 in the two sessions, with LCR Honda's Randy de Puniet 12-7 and Ben Spies 10-8 for Monster Yamaha Tech 3.

Hector Barbera ran top three at several points during the wet session, but finished only ninth (he was seventh this morning) with Simoncelli tenth in the wet.

Today saw the return of two Friday practice sessions (of 45 minutes instead of the usual one hour) in a trial system which will be reviewed following the GP. Saturday's final practice session and qualifying will also be 45-minutes, to avoid extra strain on the engines.

Aragon was called up to replace the unfinished Balatonring circuit in Hungary. It is supposed to revert to reserve status after this year's event, but few will be surprised if Aragon remains on the MotoGP calendar for 2011 and beyond.

Aragon is the third of four MotoGP rounds in Spain this year.

Friday practice (2):

1. Stoner
2. Lorenzo
3. Hayden
4. Rossi
5. Melandri
6. Dovizioso
7. de Puniet
8. Spies
9. Barbera
10. Simoncelli
11. Edwards
12. Bautista
13. Pedrosa
14. Kallio
15. Espargaro
16. Aoyama