Audi opened its account at the Austin round of the FIA World Endurance Championship by topping both Thursday practice sessions.
Loic Duval set the fastest lap during the afternoon and evening runs in the R18 he shares with Lucas di Grassi and Oliver Jarvis.
In the first session the Frenchman turned in a time of 1:48.453s, while under darkness he improved to a 1:47.235.
The majority of quicker times were recorded during the evening when the track was cooler.
Second in the timesheets after day one was the sister Audi driven by Marcel Fassler, Andre Lotterer and the returning Benoit Treluyer. A 1:47.330s effort from Lotterer wasn’t quite enough to eclipse Duval, but it did confirm the single lap pace of Audi’s high-downforce aerodynamics package.
Porsche ended Thursday the second quickest manufacturer, with Brendon Hartley registering a 1:47.959s best in the Mexico-winning 919 Hybrid. That put Porsche around seven tenths down on Audi heading into Saturday’s qualifying session.
The Toyota TS050s continued to struggle in matching their early season pace, with both cars failing to challenge Porsche and Audi on the opening day.
Sebastien Buemi got closest with a 1:48.132s attempt in the #5 car, while the #6 machine trailed by two seconds.
ByKolles Racing beat Rebellion Racing in the privateer LMP1 times, with Oliver Webb setting a 1:54.361 aboard the CLM-engined P1/01.
In LMP2, the championship-leading Signatech Alpine squad continued its form at the sharp end by leading the class order in practice. American driver Gustavo Menezes, driving on home soil in the WEC for the first time, clocked a 1:56.318s lap to top the group by 0.216 seconds.
Second fastest was Bruno Senna in the RGR Sport by Morand Ligier-Nissan, while a further half second back was Alex Brundle in the G-Drive Racing ORECA-Nissan.
The best daytime lap was a 1:57-flat set by G-Drive’s Rene Rast, which put the WEC LMP2 field 1.813 seconds clear of the quickest time set during IMSA WeatherTech Sportscar Championship opening practice.
GTE-Pro saw Ford top the timesheets following a balance of performance ruling against the Aston Martins which were dominant in Mexico.
Stefan Mucke’s evening time of 2:04.714s put the #66 car in front; one tenth of second shy of the IMSA pace.
Nicki Thiim finished the day second in the #95 Aston Martin – 0.782 seconds down on the leading Ford – while Gianmaria Bruni clocked the third best lap during the morning session in the #51 Ferrari 488.
Aston Martin Racing led the way in GTE-Am, with Pedro Lamy’s 2:06.092s marker enough to see off Ricky Taylor’s morning benchmark for Corvette by 1.320 seconds.
A third free practice session on Friday morning will set up qualifying in the afternoon, with the GT cars bookmarked to roll off at 17:45 local time.