Peugeot's Stephane Sarrazin returned to the top of the times in the wet warm-up session for the Petit Le Mans 10-hour race at Road Atlanta.
The Frenchman set a time of 1m20.300s ahead of Allan McNish's Audi R15 TDI, 0.605s behind.
Rob Bell was an impressive third fastest in the Drayson Lola, though he was 1.8s slower than the two diesels in front of him.
Lucas Luhr's Audi, Gil de Ferran's Acura and poleman Nicolas Minassian in the sister Peugeot completed the top six.
David Brabham was ninth fastest in the Highcroft Acura, which was built up around a new tub overnight following Scott Sharp's massive accident on Thursday. The car completed eight laps ahead of its start from the back of the grid.
Heavy overnight rain and continuing drizzle drenched the track, but despite this the only significant incident was an early red flag when the GT pole winning Robertson Doran Ford shed its engine cowling on the run to Turn 6. The bodywork was then tagged by Jaime Melo's Risi Ferrari.