The final MotoGP race weekend of the 2012 season got off to a wet start at Valencia on Friday morning.

The newly resurfaced track was soaking throughout, with Ducati's Nicky Hayden - who clinched the world title at Valencia in 2006 - and Repsol Honda's Dani Pedrosa exchanging the top spot from the eleventh minute onwards.

The American eventually pushed one-second clear of Pedrosa on his final lap, by which time the 2012 championship runner-up was already in the pits.

Yamaha's newly crowned double world champion Jorge Lorenzo moved into a late third place (+1.460s) with Andrea Dovizioso replicating his championship position in fourth (+1.536s) for Monster Yamaha Tech 3.

Fresh from a dream sixth successive victory in his final home Australian appearance, Casey Stoner made a careful start to his final MotoGP weekend with tenth (+3.042s).

While the top four championship places - Lorenzo, Pedrosa, Stoner and Dovizioso - are already decided, 14 points cover Alvaro Bautista, Valentino Rossi and Cal Crutchlow in fifth, sixth and seventh.

Bautista was fifth quickest for San Carlo Honda Gresini this morning, just ahead of Aspar's top CRT rider Aleix Espargaro, with Rossi seventh - at the start of his last weekend with Ducati - and Crutchlow eighth.

Espargaro's team-mate Randy de Puniet was the other top ten rider this morning, in ninth.

Lorenzo's team-mate Ben Spies is missing his final Yamaha appearance due to recent shoulder surgery and has been replaced by test rider Katsuyuki Nakasuga.

Nakasuga fell on his way to 13th this morning, with James Ellison (19th) the only other faller, at the start of his last event with PBM.

Former 250cc world champion and MotoGP rider Hiroshi Aoyama is returning to the premier-class in place of the injured Yonny Hernandez at Avintia Blusens for Valencia.

Aoyama, who will be a full-time Avintia rider in 2013, was 22nd and last this morning, almost ten-seconds off the pace of Hayden and two-seconds behind next slowest Claudio Corti.

Corti, dropped by the Italtrans Moto2 team in favour of Toni Elias after Aragon, is making his MotoGP debut as a wild-card for Avintia - albeit on the Kawasaki-powered Inmotec chassis - ahead of a full-time campaign with Forward Racing in 2013.

25-year-old Italian Corti took his first grand prix podium in the wet at Le Mans this year.

Second practice takes place this afternoon.

Friday practice (1):

1. Nicky Hayden
2. Dani Pedrosa
3. Jorge Lorenzo
4. Andrea Dovizioso
5. Alvaro Bautista
6. Aleix Espargaro
7. Valentino Rossi
8. Cal Crutchlow
9. Randy De Puniet
10. Casey Stoner
11. Stefan Bradl
12. Karel Abraham
13. Katsuyuki Nakasuga
14. Michele Pirro
15. Ivan Silva
16. Danilo Petrucci
17. Hector Barbera
18. Colin Edwards
19. James Ellison
20. Roberto Rolfo
21. Claudio Corti
22. Hiroshi Aoyama