Danica Patrick topped the opening practice session for this weekend's IndyCar season finale at Las Vegas.
The Andretti Autosport driver, who is making her final IndyCar appearance ahead of a full-time switch to NASCAR competition next year, was one of the last drivers out on-track.
However, her time of 24.735s with 10 minutes remaining proved enough to secure the top spot for the American.
With a few minutes to go she headed Ryan Hunter-Reay, Mike Conway and Marco Andretti in a top-four lock-out by the Andretti squad, however, a flurry of quick laps late on changed the order significantly.
Oriol Servia lapped 0.077s slower than Patrick to go second in his Newman/Haas Dallara, while Hunter-Reay and Conway rounded out the top five; the pair split by Chip Ganassi driver Scott Dixon.
Helio Castroneves was the top Penske driver in sixth, ahead of Andretti and his team-mate Ryan Briscoe.
Championship contenders Dario Franchitti (Ganassi) and Will Power (Penske) were only ninth and 14th while Ed Carpenter, who was quickest at the halfway point of the session, fell to 13th in his Sarah Fisher entry.
The session was put under full-course caution for over half an hour after fluid leaked out of the back of Ernesto Viso's KV car onto the track, and had to be cleaned up.
Pos Driver Team Time Gap 1. Danica Patrick Andretti 24.734s 2. Oriol Servia Newman/Haas 24.811s + 0.077s 3. Ryan Hunter-Reay Andretti 24.827s + 0.092s 4. Scott Dixon Ganassi 24.849s + 0.114s 5. Mike Conway Andretti 24.863s + 0.129s 6. Helio Castroneves Penske 24.868s + 0.133s 7. Marco Andretti Andretti 24.869s + 0.134s 8. Ryan Briscoe Penske 24.872s + 0.137s 9. Dario Franchitti Ganassi 24.874s + 0.139s 10. Graham Rahal Ganassi 24.941s + 0.205s 11. Charlie Kimball Ganassi 24.942s + 0.206s 12. Tony Kanaan KV 24.966s + 0.232s 13. Ed Carpenter Sarah Fisher 24.996s + 0.261s 14. Will Power Penske 25.013s + 0.278s 15. James Hinchcliffe Newman/Haas 25.016s + 0.281s 16. Vitor Meira AJ Foyt 25.036s + 0.301s 17. Takuma Sato KV 25.042s + 0.308s 18. Simona de Silvestro HVM 25.055s + 0.320s 19. Pippa Mann Rahal Letterman Lanigan 25.074s + 0.340s 20. Wade Cunningham AFS/Sam Schmidt 25.343s + 0.343s 21. Paul Tracy Dragon 25.099s + 0.364s 22. Dan Wheldon Bryan Herta/Sam Schmidt 25.101s + 0.366s 23. Alex Tagliani Sam Schmidt 25.103s + 0.368s 24. JR Hildebrand Panther 25.110s + 0.376s 25. Ana Beatriz Dreyer & Reinbold 25.120s + 0.385s 26. Buddy Rice Panther 25.151s + 0.416s 27. Tomas Scheckter Sarah Fisher 25.167s + 0.422s 28. Davey Hamilton Dreyer & Reinbold 25.199s + 0.465s 29. Sebastian Saavedra Conquest 25.204s + 0.469s 30. Townsend Bell Dreyer & Reinbold 25.221s + 0.486s 31. Alex Lloyd Dale Coyne 25.233s + 0.498s 32. EJ Viso KV 25.280s + 0.548s 33. James Jakes Dale Coyne 25.316s + 0.581s 34. Jay Howard Rahal Letterman Lanigan 25.327s + 0.592s