The Jaguar E-types had been outgunned by the AC Cobras in dry qualifying and William Paul started the car he shared with Priaulx from 13th.
He kept the car in contention while Marino Franchitti led the early damp-but-drying running in the Bryant family Cobra.
The pack was brought back together when Brian Caudwell’s Cobra got beached in the Lavant gravel, bringing out the safety car.
Bill Shepherd’s Cobra overtook Richard Kent’s E-type at the restart to run behind Franchitti, after which most of the frontrunners peeled into the pits for their mandatory stops.
Kent’s co-driver Nicolas Minassian emerged ahead of Romain Dumas in the Shepherd Cobra and Oliver Bryant (in for Franchitti) but Dumas powered past the E-type on the out-lap.
At this point, two-time Le Mans winner Dumas looked set to win. He recorded the fastest lap of 1m24.162s, quicker than his pole time, as he pulled away.
Bryant soon went by Minassian, who started to slip down the field, while the yet-to-stop Benoit Treluyer led in the Chevrolet Corvette Stingray of Nick Jarvis.
Alex Buncombe (Cobra) and Andrew Jordan (Bizzarrini) then crashed heavily at Madgwick in separate accidents as the rain returned. Both emerged unscathed but a safety car was called that turned into a red flag.
The race restarted behind the safety car with 20 minutes left on the clock, with Priaulx lining up 11th. But the heavy rain returned, hampering the Cobras with their leaf spring suspension compared to the E-types’ independent rear suspension.
Treluyer fell off at Lavant behind the safety car, handing the lead to Dumas for the restart, chased by Tom Kristensen (Lister-Jaguar coupe) and Bryant.
As Kristensen fell back to sixth before spinning from contention at Madgwick, Bryant overtook Dumas and pulled away at the front, leaving Dumas under threat from Minassian and a charging Priaulx, who had scythed to fourth.
Once ahead of Dumas’s Cobra, the well-balanced Jaguars closed on Bryant. Priaulx appeared to inadvertently hit the rear of a sideways Minassian at Fordwater, taking second as the Frenchman gathered up the moment.
Priaulx then surged past a struggling Bryant into Lavant to lead with 10 minutes to go. Minassian soon followed through into second, but could make no impression on Priaulx, who took the flag 9.9s clear in a Jaguar 1-2.
“The car was fantastic in the rain and we pushed like crazy,” said Priaulx.
Bryant completed the podium, while Dumas just held off the similar Cobra of three-time British Touring Car champion Gordon Shedden for fourth.
