The 19-time Isle of Man TT winner took the opportunity to fill in for injured America Brandon Paasch this weekend, who suffered a broken scaphoid in a crash at Snetterton in the previous round.
Dunlop, who misses this weekend’s Cookstown 100 road races as a result, ventured out in the wet morning session and set the 11th fastest time on the factory-supported Triumph, with team-mate Kyle Smith topping the times in FP1 from Donegal’s Rhys Irwin.
A number of leading riders opted to wait until the dry afternoon session, when Gearlink Kawasaki’s Ben Currie led the way by 0.150s from Harry Truelove.
Dunlop was 15th in the Supersport class in FP2 as he continues to familiarise himself with the Triumph, which is prepared by Simon Buckmaster's PTR outfit.
Dublin’s Jack Kennedy was fourth quickest while Lee Johnston, who sealed his maiden British Supersport success at Snetterton, was seventh on the Ashcourt Racing Yamaha.
Scott Swann, who made a rare appearance at last weekend’s Ulster Superbike meeting at Kirkistown, was ninth with Eunan McGlinchey (Gearlink Kawasaki) 11th.
The Supersport sprint race takes place on Saturday at 5pm with the feature race on Sunday scheduled for 3.40pm.