Peugeot had the early edge as testing for the 2011 Petit Le Mans began at Road Atlanta on Sunday.
The four factory cars from leading contenders Peugeot and Audi were among the 23 crews that attended the first seven-hour test day, with #7 Peugeot drivers Sebastien Bourdais, Simon Pagenaud and Anthony Davidson setting the pace with a 1m08.291s.
The sister car of Franck Montagny, Stephane Sarrazin and Alex Wurz was 0.519 seconds, while Dindo Capello, Tom Kristensen and Allan McNish were the top Audi line-up in third in the #2 car, 1.149s down on the lead Peugeot's time. Audi's second car completed the top four.
Leading American Le Mans Series entry - and petrol runner - was the #20 Dyson Lola-Mazda of Steven Kane, Butch Leitzinger and Humaid Al Masaood in fifth.
Level 5's HPD chassis topped LMP2 in eighth overall.
Several of the big hitters in the GT class chose to hold off joining testing until later in the week, with BMW and the top Ferrari teams not on track on Sunday. The Corvettes were quickest of those in action, ahead of the Flying Lizard and Falken Porsches.
Further tests take place on Monday and Wednesday before official practice commences on Thursday.