Conway lapped the 3.74-mile 17-turn course in 1min46.212sec over the course of 27 laps to lead Ganassi’s Renger van der Zande by 0.4sec by the end of the hour-long session.

Meyer Shank Racing’s Acura ARX-05 was third fastest in Dane Cameron’s hands, despite causing a red flag when it stopped on the front straight, while Tristan Vautier was fourth in the JDC-Miller Motorsports Cadillac.

Defending IMSA WeatherTech SportsCar Prototype champion Ricky Taylor clocked fifth fastest in the Wayne Taylor Racing Acura, albeit 1.2sec from Conway, while the AXR’s second entry, for only the Michelin Endurance Cup rounds, was fifth thanks to 2016 IndyCar champion Simon Pagenaud.

The #55 Mazda that won last November’s Sebring 12H finished the opening session seventh.

Mikkel Jensen did a predictably strong job for PR1 Mathiasen Motorsports in LMP2, his best time just 2sec behind the DPi Mazda, but no less impressive was the returning Guy Smith – in his first Sebring outing since 2013! – 0.8sec in arrears in the United Autosports entry, eclipsing third placed Thomas Merrill (WIN Autosport) by 1.8sec.

Jordan Taylor’s best effort in the #3 Corvette C8.R – a 1min56.715sec – put him ahead of all the LMP3 entries, and 0.559sec ahead of Mathieu Jaminet in the WeatherTech Racing Porsche 911 RSR.

Tommy Milner was third in the second Corvette, with the two BMW M8s completing the class.

Jeroen Bleekemolen (Riley Motorsports) and Colin Braun (CORE autosport) were class of the LMP3 field, just 0.075sec apart, but their Ligiers were very closely pursued by the chasing pack, the top five covered by just 0.4sec.

The irrepressible Bill Auberlen topped GT Daytona for Turner Motorsports (BMW M6) with Jack Hawksworth (Vasser Sullivan Lexus), Frank Perera (Grasser Racing Lamborghini), Earl Bamber (Team Hardpoint EBM Porsche 911) and Maro Engel (Sun Energy1 Mercedes AMG GT3) ensuring five different marques in the top five.

Second practice begins at 1.55pm local (Eastern) time.