Daniil Kvyat ended the first day of GP3 testing at Estoril on Tuesday on top of the timesheets.
The MW Arden driver was second fastest in the morning session, behind Manor's Tio Ellinas. But the Red Bull-backed Russian then responded with the best time of the day with an hour of the afternoon remaining.
His 1m30.902s lap gave the Formula Renault NEC champion a 0.122s advantage over Ellinas, the Cypriot having himself knocked Lewis Williamson's Atech CRS car off the top spot just a minute earlier.
Williamson wound up third, ahead of MW Arden's David Fumanelli and Robert Visoiu, who was having a run-out with the ART-run Lotus squad.
British Formula 3 champion Jack Harvey was sixth fastest for Carlin while Adderly Fong, Eric Lichtenstein, Alex Brundle and Giovanni Venturini - who was afflicted by brake problems - completed the top 10.
There were several other red flags during the day, Mario Marasca spinning his Trident car at Turn 8 early on and Miki Weckstrom and Eric Lichtenstein stopping due to a spin and a technical problem respectively.
Alex Fontana caused the final stoppage as he hit a bump at Turn 2 and spun, damaging the front of his Jenzer car and bringing an early end to his day.
This year's champion Mitch Evans was also at Estoril, testing the new uprated GP3 car that will make its debut in 2013. His laps were not timed.
Pos Driver Team Time Gap
1. Daniil Kvyat MW Arden 1m30.902s
2. Tio Ellinas Manor 1m31.024s + 0.122s
3. Lewis Williamson Atech CRS 1m31.131s + 0.229s
4. David Fumanelli MW Arden 1m31.248s + 0.346s
5. Robert Visoiu MW Arden 1m31.365s + 0.463s
6. Jack Harvey Carlin 1m31.430s + 0.528s
7. Adderly Fong Manor 1m31.465s + 0.563s
8. Eric Lichtenstein Carlin 1m31.555s + 0.653s
9. Alex Brundle Lotus 1m31.580s + 0.678s
10. Giovanni Venturini Status 1m31.597s + 0.695s
11. Miki Weckstrom Status 1m31.703s + 0.801s
12. Mario Marasca Trident 1m32.240s + 1.338s
13. Meindart van Buuren Atech CRS 1m32.287s + 1.385s
14. Roberto la Rocca Atech CRS 1m32.364s + 1.462s
15. Alex Fontana Jenzer 1m32.441s + 1.539s
16. Samin Gomez Jenzer 1m32.577s + 1.675s
17. Emanuele Zonzini Lotus 1m32.944s + 2.042s
18. Ryan Cullen Status 1m33.723s + 2.821s
19. Emanuele Piva Trident 1m33.865s + 2.963s
20. Sheban Siddiqi Lotus 1m37.630s + 6.728s