James Hinchcliffe opened IndyCar's race weekend at Milwaukee by setting the fastest time in the opening practice session on Saturday.
The Canadian moved to the top 15 minutes into the session with a fastest speed of 165.451mph (22.0851s) and his time was still unbeaten when the chequered flag waved three-quarters of an hour later.
Ganassi's Ryan Briscoe came closest ahead with a best lap average of 165.349mph (22.0987s), leaving Hinchcliffe's Andrett team-mate Ryan Hunter-Reay in third.
Josef Newgarden and Tony Kanaan completed the top five.
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With rookies and drivers outside the top 10 in points having an extra set of tyres to work with, those in championship contention left it to others to rubber the track in before venturing out of the pitlane.
Points leader Will Power made his first appearance with 30 minutes remaining and finished up 11th fastest, three places ahead of team-mate and closest title rival Helio Castroneves.
The morning was interrupted twice by yellow flags; the first coming 38 minutes into the session for a track inspection, and the second being prompted by Carlos Munoz experiencing an electrical problem and coming to a stop on the track five minutes before the end.
Pos Driver Team/Engine Time Gap Laps
1. James Hinchcliffe Andretti/Honda 22.0851s 31
2. Ryan Briscoe Ganassi/Chevy 22.0987s +0.0136s 24
3. Ryan Hunter-Reay Andretti/Honda 22.1075s +0.0224s 44
4. Josef Newgarden Fisher/Honda 22.1894s +0.1043s 50
5. Tony Kanaan Ganassi/Chevy 22.1955s +0.1104s 26
6. Scott Dixon Ganassi/Chevy 22.2604s +0.1753s 39
7. Juan Pablo Montoya Penske/Chevy 22.3241s +0.2390s 29
8. Carlos Munoz Andretti/Honda 22.3336s +0.2485s 32
9. Mikhail Aleshin Schmidt/Honda 22.3484s +0.2633s 38
10. Simon Pagenaud Schmidt/Honda 22.3557s +0.2706s 36
11. Will Power Penske/Chevy 22.3770s +0.2919s 43
12. Charlie Kimball Ganassi/Chevy 22.4153s +0.3302s 48
13. Graham Rahal Rahal/Honda 22.4320s +0.3469s 48
14. Helio Castroneves Penske/Chevy 22.4910s +0.4059s 35
15. Justin Wilson Coyne/Honda 22.5014s +0.4163s 40
16. Takuma Sato Foyt/Honda 22.5037s +0.4186s 42
17. Sebastien Bourdais KV/Chevy 22.5771s +0.4920s 39
18. Marco Andretti Andretti/Honda 22.5932s +0.5081s 25
19. Sebastian Saavedra KV/Chevy 22.6405s +0.5554s 43
20. Ed Carpenter Carpenter/Chevy 22.7251s +0.6400s 38
21. Carlos Huertas Coyne/Honda 22.8352s +0.7501s 53
22. Jack Hawksworth Herta/Honda 22.8909s +0.8058s 47
All drivers use Dallara chassis