Ryan Briscoe was quickest by a relatively comfortable 0.1496sec margin in morning practice for the Chicagoland IndyCar round.
The Penske driver's 25.1154sec lap in the closing moments saw him depose previous pacesetter Scott Dixon (Ganassi).
Championship leader Will Power was third for Penske, ahead of Andretti Autosport's four cars, led by Marco Andretti. Both Andretti and teammate Ryan Hunter-Reay (who was sixth in between Danica Patrick and Tony Kanaan) had led the session at times earlier.
Penske's other driver Helio Castroneves was eighth, with Dixon's Ganassi teammate Dario Franchitti back in 10th. They were split by a strong run from KV's EJ Viso.
Of the drivers returning to the series this weekend, Tomas Scheckter was 17th for Conquest, while Mike Conway's latest substitute Ana Beatriz took 22nd in her Dreyer & Reinbold car, and Davey Hamilton was 27th for De Ferran Dragon.
But Vision/Panther Racing's Ed Carpenter will go into qualifying later today with scant preparation having brushed the wall and caused a yellow on only his fifth lap of the session, leaving him in the pits thereafter.
Pos Driver Team Time Gap
1. Ryan Briscoe Penske 25.1154s
2. Scott Dixon Ganassi 25.2650s + 0.1496s
3. Will Power Penske 25.2716s + 0.1562s
4. Marco Andretti Andretti 25.2801s + 0.1647s
5. Danica Patrick Andretti 25.2812s + 0.1658s
6. Ryan Hunter-Reay Andretti 25.2902s + 0.1748s
7. Tony Kanaan Andretti 25.3075s + 0.1921s
8. Helio Castroneves Penske 25.3084s + 0.1930s
9. EJ Viso KV 25.3100s + 0.1946s
10. Dario Franchitti Ganassi 25.3106s + 0.1952s
11. Graham Rahal Newman/Haas 25.3471s + 0.2317s
12. Dan Wheldon Panther 25.3768s + 0.2614s
13. Alex Lloyd Dale Coyne 25.3893s + 0.2739s
14. Vitor Meira AJ Foyt 25.4334s + 0.3180s
15. Bertrand Baguette Conquest 25.4653s + 0.3499s
16. Hideki Mutoh Newman/Haas 25.4892s + 0.3738s
17. Tomas Scheckter Conquest 25.4952s + 0.3798s
18. Justin Wilson Dreyer & Reinbold 25.5017s + 0.3863s
19. Takuma Sato KV 25.5017s + 0.3863s
20. Mario Moraes KV 25.5076s + 0.3922s
21. Raphael Matos De Ferran Dragon 25.5308s + 0.4154s
22. Ana Beatriz Dreyer & Reinbold 25.5323s + 0.4169s
23. Simona de Silvestro HVM 25.5528s + 0.4374s
24. Alex Tagliani FAZZT 25.5573s + 0.4419s
25. Jay Howard Sarah Fisher 25.5854s + 0.4700s
26. Sarah Fisher Sarah Fisher 25.6063s + 0.4909s
27. Davey Hamilton De Ferran Dragon 25.6302s + 0.5148s
28. Milka Duno Dale Coyne 25.8269s + 0.7115s
29. Ed Carpenter Panther/Vision 29.3971s + 4.2817s