A stunning late effort by Aaro Vainio earned the Koiranen driver pole position for Saturday's opening GP3 race in Hungary.
The session had been dominated by the ART cars of Conor Daly, Jack Harvey and Facu Regalia when the Finn - a former ART man - produced his lap of 1m32.811s.
Daly responded but fell 0.18 seconds short. In a frantic end to the session MW Arden's Daniil Kvyat set the third best time, while the pace of the Koiranen cars was demonstrated by Kevin Korjus being fourth fastest.
Harvey dropped to fifth, just ahead of fellow Brit Lewis Williamson in the Bamboo entry.
Melville McKee produced a strong showing to line up seventh for Bamboo, while Carlos Sainz Jr dropped from third to eighth during the action-packed closing stages.
Title rivals Regalia and points leader Tio Ellinas will share the fifth row, with the ART car lining up ahead of the Cypriot's Marussia Manor entry.
Such was the strength of the field, the top 18 cars were covered by a second, boding well for an exciting race.
Pos Driver Team Time Gap 1. Aaro Vainio Koiranen 1m32.811s 2. Conor Daly ART 1m32.987s +0.176s 3. Daniil Kvyat MW Arden 1m33.070s +0.259s 4. Kevin Korjus Koiranen 1m33.104s +0.293s 5. Jack Harvey ART 1m33.109s +0.298s 6. Lewis Williamson Bamboo 1m33.200s +0.389s 7. Melville McKee Bamboo 1m33.337s +0.526s 8. Carlos Sainz Jr MW Arden 1m33.345s +0.534s 9. Facu Regalia ART 1m33.354s +0.543s 10. Tio Ellinas Manor 1m33.384s +0.573s 11. Robert Visoiu MW Arden 1m33.439s +0.628s 12. Giovanni Venturini Trident 1m33.582s +0.771s 13. Patric Niederhauser Jenzer 1m33.599s +0.788s 14. Alex Fontana Jenzer 1m33.614s +0.803s 15. Nick Yelloly Carlin 1m33.658s +0.847s 16. Dino Zamparelli Manor 1m33.715s +0.904s 17. Patrick Kujala Koiranen 1m33.778s +0.967s 18. Eric Lichtenstein Carlin 1m33.800s +0.989s 19. David Fumanelli Trident 1m33.893s +1.082s 20. Jimmy Eriksson Status 1m34.089s +1.278s 21. Josh Webster Status 1m34.237s +1.426s 22. Adderly Fong Status 1m34.241s +1.430s 23. Luis Sa Silva Carlin 1m34.952s +2.141s 24. Emanuele Zonzini Trident 1m35.006s +2.195s 25. Samin Gomez Jenzer 1m35.491s +2.680s 26. Ryan Cullen Manor 1m36.046s +3.235s 27. Carmen Jorda Bamboo 1m37.246s +4.435s