Reigning DTM champion Rene Rast went fastest in the best of the Mazda RT24-P DPi contenders right at the end of the opening 60-minute session for the IMSA WeatherTech SportsCar Championship opener.

The German ended up on a 1m37.428s, which put him just seven thousandths up on Tristan Vautier in the Spirit of Daytona Cadillac DPi-V.R.

Cadillacs filled out the next two positions with times within a tenth of Rast's mark.

Jordan Taylor took third in the Wayne Taylor Racing entry on a 1m37.452s and Filipe Albuquerque ended up fourth on a 1m37.519s in the fastest of the Action Express cars.

The performance of the Mazda, which struggled at the Roar Before the 24 test at Daytona earlier in the month, follows a series of rules tweaks in the Prototype class.

The RT24-P has been given a 15kg weight break and an 300rpm increase in revs in a Balance of Performance change.

Cadillac, which dominated at the Roar, has had its twin engine air-restrictors cut in diameter by 0.6mm.

Alex Brundle was just over a tenth off the top spot in the best of the Jota-run Jackie Chan DC Racing Oreca-Gibsons on a 1m37.530s.

Two-time Le Mans 24 Hours winner Romain Dumas took sixth in the CORE autosport Oreca.

The best of the Penske Acura ARX-05s ended up 10th in the hands of Graham Rahal on a 1m38.084s.

Sportscar debutant Fernando Alonso did not drive in the session after teammate Phil Hanson had a minor off in their United Autosports Ligier-Gibson JS P217s.

Hanson, who was fifth fastest at the time, went off at Turn 5, the car sustaining minor front-end damage.

Joey Hand led the way for Ford in the GTLM class.

The American posted a 1m44.062s in his Ganassi Ford GT, which put him nearly half a second up on second-placed Alessandro Pier Guidi in the Risi Competizione Ferrari 488 GTE.

Laurens Vanthoor was just three hundredths behind in third position at the wheel of the fastest of the CORE-run factory Porsche 911 RSRs.

Miguel Molina took top spot in the GTD division in his Risi Ferrari 488 GT3 with a best time of 1m47.223s.

First practice results (top 10):

Pos.	No.	Drivers	Chassis	Time	Gap
1	77	Oliver Jarvis René Rast Tristan Nunez	Mazda DPi	1'37.428
2	90	Matt McMurry Tristan Vautier Eddie Cheever III	Cadillac DPi	1'37.435	0.007
3	10	Jordan Taylor Ryan Hunter-Reay Renger van der Zande	Cadillac DPi	1'37.452	0.024
4	5	Christian Fittipaldi Filipe Albuquerque Joao Barbosa	Cadillac DPi	1'37.519	0.091
5	78	Ho-Pin Tung Antonio Felix da Costa Alex Brundle Ferdinand Habsburg	ORECA LMP2	1'37.530	0.102
6	54	Loic Duval Romain Dumas Jon Bennett Colin Braun	ORECA LMP2	1'37.563	0.135
7	37	Robin Frijns Daniel Juncadella Felix Rosenqvist Lance Stroll	ORECA LMP2	1'37.766	0.338
8	31	Mike Conway Eric Curran Felipe Nasr Stuart Middleton	Cadillac DPi	1'37.844	0.416
9	38	Joel Miller James French Kyle Masson Pato O'Ward	ORECA LMP2	1'37.866	0.438
10	7	Helio Castroneves Graham Rahal Ricky Taylor	Acura DPi	1'38.084	0.656