Peter Hickman edged Lee Johnston in a thrilling opening Ulster Grand Prix Supersport race by 0.357 seconds to secure his second win of the 2019 event.
The Smiths Racing rider, pictured winning his TT class above earlier this year, dominated the red-flagged first Superbike race to bag his seventh win at the Ulster GP.
He also established the Dundrod event as the fastest road race in the world with a new lap record of 136.415mph.
SSP polesitter Hickman and Johnston - Hickman's rival who also won in the class at the Isle of Man TT - duked it out from the off, with the latter getting the upper hand off the line to lead for the first tour.
The Ashcourt Racing Yamaha rider held a half a second advantage over Hickman at the end of the first tour, as a train of seven riders ran close together.
By the end of lap two, Johnston and Hickman had broken away from the pack with Hickman passing his rival on the third tour, but Johnston returned the favour towards the end of the lap to lead on the start of the fourth lap.
Hickman was just 0.103s adrift as they headed onto the final lap, and pulled off a move which would secure him his eighth Ulster GP win.
Dean Harrison struggled aboard the Silicone Engineering Kawasaki and was a distant third after early rival Davey Todd (Padgetts Honda) dropped out on the penultimate lap.
Jamie Coward (Prez Racing) pipped the sister Padgetts CBR600 of Conor Cummins by 0.088s for fourth, while Paul Jordan rounded out the top six on the Devitt Racing Yamaha.
Maiden Ulster success for Jordan in Supertwins race
The four-lap Supertwins race concluded Thursday's racing, and it was Jordan who snatched victory away from Joe Loughlin at the end by just 0.092s.
Lee Johnston's hopes of going one better in the STW race were dashed when his KMR machine failed on the penultimate lap while he was running third.
Jordan trailed Loughlin over the line to start the final lap, but he overhauled him to secure his maiden Ulster GP triumph.
Coward completed the podium.
In the Lightweight and Ultra-lightweight race, Neil Kernohan took the win in the lightweight category on his 250 Honda, while popular Czech rider Michal Dukoupil guided his Moto3 machine to ULTW honours.