JDC-Miller Motorsports has topped the time charts in the opening IMSA WeatherTech SportsCar Championship practice session for Sunday’s Sahlen’s Six Hours of The Glen.

The No. 85 Oreca 07 Gibson of Stephen Simpson was quickest in the 60-minute session, laying down a best lap of 1:35.491 to edge out the No. 2 Tequila Patron ESM Nissan Onroak DPi of Ryan Dalziel by 0.039 seconds.

Action Express Racing was third quickest with its No. 5 Cadillac DPi-V.R of Joao Barbosa, followed by the No. 55 Mazda RT24-P in fourth, thanks to Jonathan Bomarito’s 1:37.190 lap time.

The sister No. 70 Mazda, which debuts new cooling-related updates this weekend, did not set a time due to brake issues.

Championship leaders Ricky and Jordan Taylor, who head into the weekend still undefeated in Prototype competition this year, were only able to muster the 6th quickest time in the session, nearly two seconds slower than Simpson’s pace-setting time in his LMP2 car.

Ford Chip Ganassi Racing was quickest in GT Le Mans, with Dirk Mueller jumping to the top with a 1:43.078 in the No. 66 Ford GT, while Detroit class winners Michael Shank Racing led the way in GT Daytona with the No. 93 Acura NSX GT3, driven by Andy Lally.

Prototype Challenge, meanwhile, was topped by the No. 38 Performance Tech Motorsports Oreca FLM09 of Pato O’Ward.

The session ran without major incident, other than a spout of rain in the closing minutes, which resulted in most teams hitting the pit lane early.

Showers are also in the forecast for Friday’s second practice session, which gets underway at 3:30 p.m. ET.

RESULTS: Practice 1