Scott Redding bagged his fourth Bennetts British Superbike win of the season as he stormed to victory after early leader Danny Buchan crashed out of contention.
It had been a two-horse scrap for the entire first half of the race, but the Be Wiser Ducati rider put the hammer down and pocketed 25 points after FS-3 Kawasaki's race one winner binned his bike with 12 laps remaining.
But problems had already hit Buildbase Suzuki before the lights went out as Luke Stapleford looked to have bike issues and parked up his machine at the side of the track before heading into the paddock on foot.
Mackenzie grabbed the holeshot off the start as he led Buchan, Redding and Brookes away from the line, but pole man Buchan was soon back into the lead before Mackenzie ran wide at the Hairpin and allowed Redding to slide into second.
But disaster hit for the lone Tyco BMW of Christian Iddon as he lost the front at the Chicane and crashed out of eighth, prompting chiefs to deploy the safety car as he was stretchered off to the medical centre.
When it was called in at the end of lap seven, the pack bunched back up but Buchan continued to lead a breakaway trio of Redding and Mackenzie with Tommy Bridewell looking for a way ahead in fourth.
Redding powered into the lead on lap nine as the leaders crested the finish line and as Mackenzie scrambled for a way ahead on Buchan, the Scotsman lost time and allowed Bridewell through into third.
The front-running duo of Redding and Buchan broke over a second clear of the field with 12 laps in the bag, but Buchan couldn't find a way through until lap 16 when he stuck his ZX10 up the inside of Redding at Clarkes to hit the front.
Further down the order, it was another bad end for Jason O'Halloran as he was given a black and orange flag for technical problems.
But it was even worse for Buchan who lost the front at McIntyres on lap 18 and threw away a double win as Redding was handed the lead with 1.8s to spare over Mackenzie, who inherited second place.
Back down the order, Matt Truelove ran onto on the grass at Duffus, but upon rejoining the track he gave Silicone Engineering's Dean Harrison nowhere to go and the TT ace ran into the side of him as the two crashed out.
And while Redding looked on for a clear victory at the front of the field, action was brought to a halt six laps from the end and a result was declared after Brad Ray's Suzuki blew up big-style and dumped oil.
Redding snatched the win and the series lead as home hero Mackenzie took second and Oxford Ducati's Bridewell bagged third after passing the second Be Wiser bike of Josh Brookes, who crossed the line fourth.
Honda Racing's Andrew Irwin took fifth ahead of Smith's BMW man Peter Hickman, who averted disaster after dodging Ray's stricken GSX-R, while Santander Salt TAG Racing's Dan Linfoot came home seventh.
Luke Mossey took eighth for the OMG Suzuki squad while Quattro Plant JG Speedfit's Glenn Irwin pipped James Ellison for ninth.
