Click here for full WEC FP1 results from the Circuit of the Americas
Porsche has immediately picked up where it left off at the Nurburgring by storming to a comfortable 1-2 at Austin, while WEC leaders #7 Audi suffered technical issues and could only complete four laps in the opening practice session.
The German manufacturer has laid down a marker to Audi and Toyota by pulling out almost two seconds on the chasing LMP1 machines, with Romain Dumas setting the fastest lap of the session, two-tenths quicker than Mark Webber in the sister Porsche 919 Hybrid.
WEC championship leaders of Andre Lotterer, Marcel Fassler and Benoit Treluyer suffered a frustrating start in Austin its FP1 running was curtailed due to brake failures.
LMP2 front-runners KCMG also started on fine form after wins at Le Mans and the Nurburgring as it headed the category by over half a second from US team Extreme Speed Motorsports.
The #71 AF Corse Ferrari topped the timesheet in the GTE-Pro class as Patrick Dempsey's Proton Racing Porsche finished quickest in the GTE-Am category.