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Graham Rahal set the fastest time in morning practice as the IndyCar Series returned to action at Milwaukee following the Indianapolis 500.
The Newman/Haas/Lanigan driver exchanged first place with Ganassi's Scott Dixon several times early on, then remained on top despite missing part of the session while a problem with a CV joint was attended to.
Dixon also had a minor issue late in the morning as he caused a brief yellow after running out of fuel on track during his final run.
Hideki Mutoh (Andretti Green) managed to split Rahal and Dixon by the end, while Penske's Ryan Briscoe and Indy winner Helio Castroneves took fourth and sixth, separated by HVM driver EJ Viso, the latter showing encouraging form after a month of frustration at Indianapolis.
Championship leader Dario Franchitti was back in ninth in the second Ganassi car, behind KV's Mario Moraes and AGR's Tony Kanaan, who is nursing rib injuries from his massive accident last weekend.
Justin Wilson continued to demonstrate Dale Coyne Racing's oval gains by claiming the final top ten spot, ahead of leading rookie Mike Conway (Dreyer & Reinbold).
The session was extended by several minutes to make up for the time lost when Stanton Barrett backed his 3G Dallara-Honda into the wall on the exit of Turn 2 during the opening half-hour of practice for rookies and drivers outside the top ten in the championship. Barrett's accident caused damage to the SAFER barrier and was a further blow to 3G after its Indy non-qualification, although fortunately Barrett escaped unhurt.
Dan Wheldon was another driver who only had very limited mileage. A steering rack problem became apparent before he had set a flying lap, and he was only able to join the session for the final ten minutes.
Tomas Scheckter did not get to run at all in what should have been his first session as a Dreyer & Reinbold driver. The South African's car had a fuel pump issue on its installation lap and had to return to the paddock for the rest of the morning.
Paul Tracy began his sojourn at AJ Foyt's team with a low-key 17th place while working to fine-tune the car's set-up.