On the series’ debut on the tight and twisty 1.654-mile, nine-turn temporary street circuit in downtown Detroit, Eng beat Nick Tandy’s Porsche and Cadillac’s Sebastien Bourdais to the fastest time in this two-hour session for GTP and GTD Pro cars.

The FP1 pacesetting #6 Porsche Penske Motorsport 963 of Tandy and Mathieu Jaminet was given a 10-minute hold at the start of the session due to a tire carryover infringement. The early stages were interrupted anyway by a red flag after the #64 Ford Mustang GTD entry of Harry Tincknell went off at Turn 1.

The #7 sister PPM car of Dane Cameron set the benchmark at 1m07.372s before being pipped by Pipo Derani’s Action Express-run Cadillac V-Series.R on 1m07.308s, who took a trip down the Turn 1 runoff after setting the fastest time.

Renger van der Zande then made it a Caddy 1-2 in the #01 Chip Ganassi Racing-run example, beating Derani’s time by 0.156s with 1m07.152s. Another red flag was waved just after van der Zande visited the Turn 8 runoff.

Cameron restored Porsche’s advantage by lapping in 1m07.120s just before Jaminet went even faster with 1m07.063s in the #6 car. Cameron’s response was a 1m06.600s as the session ticked into its second hour, four tenths clear of van der Zande and Jesse Krohn (#24 BMW M Hybrid V8) and Jaminet.

Felipe Nasr took over the pacesetting #7 Porsche from Cameron but immediately copped a drive-through penalty for a pit exit violation, just before a third, very brief, red flag.

Jack Aitken (in the AXR Caddy in place of Derani) vaulted up to second, 0.376s away from Cameron’s top time, before Filipe Albuquerque’s Wayne Taylor Racing with Andretti Acura ARX-06 beat that with 1m06.882s to go P2 instead.

A fourth red flag was required to retrieve the stranded Pfaff McLaren GTD car of Oliver Jarvis from the Turn 1 runoff. That set up a final 20 minutes of practice before qualifying later, and Sebastien Bourdais (#01 Cadillac) was the next to take a shot at Cameron’s time, falling short by 0.274s

Nick Yelloly finally toppled Cameron in his #25 RLL-run BMW M Hybrid V8, recording a 1m06.482s, before Eng beat that by 0.134s in the #24 sister car with 1m06.348s.

Into the closing moments, Bourdais split the BMWs with 1m06.470s, before Tandy got to within exactly a tenth of Eng to grab P2.

Bourdais dropped to third, ahead of Yelloly, Nasr, Ricky Taylor (#10 Acura), Aitken, Jordan Taylor (#40 Acura), Bent Viscaal (Proton Porsche) and Tijmen van der Helm (JDC-Miller Porsche).

Corvette 1-2 in GTD Pro

In GTD Pro, Antonio Garcia set the early pace at 1m10.009s in his #3 Corvette Z06 GT3.R, with Tommy Milner making it a Chevy 1-2 in the #4 sister car – albeit a quarter of a second away from his team-mate’s pace.

Garcia chipped away at his fastest time, working down to 1m09.821s, but Milner later beat that with 1m09.654s.

Seb Priaulx was best of the rest in AO Racing’s #77 Porsche 911 GT3 R, 0.229s off the pace of the Corvettes.