The Czech pilot, whose best placing in the Championship was his second position last year, clocked a qualifying time of 50.876sec at the Texas Motor Speedway in Fort Worth.

By contrast, overall leader Michael Goulian of the United States, who leads Sonka by five points, could only manage ninth place in qualifying in 51.708.

Australia's Matt Hall, the 2015 and 2016 Championship runner-up who is currently two points behind Sonka, finished fifth in 51.284.

With 15 points on offer to the winner in this deciding race, any one of the three contenders could swoop to claim the trophy for a first time.

Goulian's victory in the last month's race at Indianapolis ended a run of three consecutive victories for Sonka and lifted him ahead of his Czech rival.

Sonka will be hoping his performance in qualifying - where he was beaten only by Germany's 2016 champion Matthias Dolderer, who clocked 50.614 - will tell in the final reckoning.

That said, he also topped qualifying for the Indianapolis race.