Casey Stoner led the way during first free practice for the Indianapolis MotoGP, during a session briefly red flagged after a highside for Hector Barbera.

After a two weekend summer break, MotoGP action resumed in dry and bright conditions, albeit on a track still damp in places after heavy overnight rain.

Those patches, and the lack of track use on the infield section, meant grip levels were low and reigning champion Stoner's best time - set on his 13th of 14 laps - was three seconds off his own official circuit best.

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Repsol Honda team-mate Dani Pedrosa also spent substantial time on top of the standings and finished the session just 0.181s from Stoner, with Ducati's Nicky Hayden snatching third (+0.547s) on his final lap.

Fellow American Ben Spies was the top Yamaha rider in fourth (+0.611s) at a circuit where he has been on the rostrum for the past two seasons.

Honda LCR rookie Stefan Bradl made a quick start to the session before being pushed back to fifth (+1.102s) with fellow satellite RCV rider Alvaro Bautista taking sixth for Gresini.

Cal Crutchlow fell from his Tech 3 Yamaha early in the session after an unseen incident, before returning to take seventh, with Yamaha's world championship leader Jorge Lorenzo just eighth and 1.387s off the pace of Stoner.

The poor track conditions mean the Spaniard is unlikely to be alarmed. Lorenzo holds a 23 point lead over Pedrosa and 32 point advantage over Stoner.

Valentino Rossi, riding in his first event since announcing a return to Yamaha for 2013, steered his Ducati to ninth place (+1.420s) with Barbera credited with tenth despite his end-of-session absence.

The Spaniard, who broke his left tibia and fibula less than a month ago, halted the session with eleven minutes remaining after a highside at the final turn.

Barbera had clipped the kerb as he made the right/left change of direction that leads onto the home straight - causing the rear of his Pramac Ducati to swing around and fling Barbera over the front.

Slow to get up, an ambulance was sent to take the Spaniard to the medical centre, where he complained of chest rather than leg pain. Toni Elias is on standby should Barbera be unable to continue.

Crutchlow's team-mate Andrea Dovizioso was ranked behind Barbera in eleventh, with Avintia's Yonny Hernandez the leading CRT ride in twelfth place, 2.4s from Stoner.

Team-mate Ivan Silva also lapped quicker than the slowest manufacturer rider, Karel Abraham (Cardion AB).

Colin Edwards was 19th for Forward Racing, which is continuing with the Suter-BMW this weekend.

Two home wild-card CRT entries are present at Indy: Steve Rapp (Attack Performance), who took part in the previous Laguna Seca round but failed to qualify, plus fellow AMA veteran Aaron Yates, who is making his MotoGP debut for GPTech.

Rapp was 20th (+4.694s) and Yates, whose Suzuki-powered bike is painted in a Rizla-style light blue, 23rd and last (+6.129s). Both have recently tested at Indy.

Second practice will take place this afternoon.

No rider has yet won twice at Indianapolis, with Rossi, Lorenzo, Pedrosa and Stoner the former event winners.

Friday practice (1):

1. Casey Stoner
2. Dani Pedrosa
3. Nicky Hayden
4. Ben Spies
5. Stefan Bradl
6. Alvaro Bautista
7. Cal Crutchlow
8. Jorge Lorenzo
9. Valentino Rossi
10. Hector Barbera
11. Andrea Dovizioso
12. Yonny Hernandez
13. Aleix Espargaro
14. Karel Abraham
15. Mattia Pasini
16. Randy De Puniet
17. Ivan Silva
18. Michele Pirro
19. Colin Edwards
20. Steve Rapp
21. Danilo Petrucci
22. James Ellison
23. Aaron Yates