Before Monday’s Supersport race, only Dunlop’s legendary uncle Joey Dunlop and John McGuinness had pushed their tally of wins into the 20s.
But Dunlop prevailed in a strong challenge from previous class winner Harrison to claim his first win of the week.
Predicted to be the closest class of race week, the Supersport race – shortened from four to three laps due to the rescheduled Sidecar contest being run today – got underway at 10:45am local time with TT legend John McGuinness leading them off on his SMT Honda.
But at the first sector split at Glen Helen it was MD Racing’s Dunlop – who set off at number six - on his Yamaha who led Harrison by 1.4 seconds.
Dunlop got that gap out to 2.5s on the run through Ballaugh, with Lee Johnston on the Ashcourt Racing Yamaha slotting into third ahead of Peter Hickman on the Trooper Beer Triumph.
Harrison, who made a last-minute switch to Metzeler from Dunlop tyres ahead of the race, rallied through the Bungalow section on his DAO Racing Kawasaki to close to within 1.8s, but Dunlop led him by 3.2s as he came to the end of the lap and into the pits for his fuel stop.
But a slightly slow stop cost Dunlop time, with his advantage over Harrison 1.5s through Glen Helen on the second tour.
Harrison twice got Dunlop’s lead down to under a second, with the gap 1.1s as they flew through the Grandstand to start the final lap.
At Glen Helen, Harrison fired in a sector record for the Supersport class to run just 0.1s behind Dunlop on corrected time.
Dunlop nudged that back out to 0.3s at the Ballaugh split and dug deep on the run through Ramsey to rebuild his advantage to 2.6s.
Over the mountain section Dunlop’s lead swelled above three seconds, with the Ulsterman taking the chequered flag by 5.6s from Harrison for his eighth win in the Supersport class and with it a new class lap record of 129.47mph.
Hickman ended the opening lap in fourth, but overhauled Johnston after a slow stop for the Ashcourt Racing rider, before taking third away from OMG Racing’s James Hillier on his Yamaha.
With Saturday’s Superbike winner Hickman in third, Johnston was 3.5s adrift in fourth ahead of Hillier – who will not race in this afternoon’s Superstock TT due to an unspecified technical infringement forcing the team to withdraw his Yamaha from the race.
Jamie Coward was sixth on his KTS Yamaha, 17.2s behind Hillier, with Conor Cummins seventh ahead of Padgetts Honda team-mate Davey Todd – who was expected to be a contender in this race.
Cowton Racing’s Dominic Herbertson and Russell Racing’s Ian Hutchinson completed the top 10, while McGuinness was a distant 16th.
The race was red-flagged late on and after the leaders had seen the chequered flag due to an incident.
