William Dunlop fought tooth and nail with his brother Michael to clinch his first international Superbike victory at the North West 200.
In wet conditions, Dunlop on the Tyco Suzuki quickly caught and passed early leader Ian Hutchinson on the Milwaukee Yamaha and stretched an advantage at the front on the GSX-R1000.
Manx rider Conor Cummins was holding third on the Honda Racing Fireblade followed by Michael Rutter on the Bathams BMW and Dan Kneen.
Pole man Michael Dunlop, though, was the rider on the move as he came through from a poor start to climb the order, eventually slotting into third position on lap three at Ballysally on the BMW Motorrad S1000RR.
The race had been cut from seven laps to five due to the conditions and time was running out for Dunlop as he chased his brother William, who led by four seconds at the start of the penultimate lap.
However, the 25-year-old now had the Tyco Suzuki rider in his sights after passing Cummins to move into second and on the final lap had closed onto the rear wheel of the Suzuki.
The BMW rider made his move into Metropole to take the lead for the first time but in a nail-biting finish, long time race leader Dunlop hit back with a superb move on the brakes into Juniper Hill chicane and wrapped up his fourth North West 200 victory by half a second.
Cummins was a comfortable third followed by Rutter, Hutchinson, Simon Andrews, Gary Johnson on the Lincs Lifting Honda and Brookes.
Tyco Suzuki's Guy Martin and Austrian rider Horst Saiger completed the top ten.