James Ellison has taken his first British Superbike Championship win since the opening round of the season after mastering treacherous conditions at Silverstone.
The Swan Honda rider, who finished fourth in the damp opening encounter, made the most of his improved starting position to snatch the lead from the start and cruise away to win by almost six seconds.
Ellison, who has embarked on a steady return to form since breaking his leg at Thruxton back in April, was barely challenged throughout the race, which was shortened due to the delays in the schedule.
Indeed, Kiyonari put up a stern fight initially but decided to settle for a good points' haul in second rather than challenge Ellison on the slippery surface.
A good event for HM Plant Honda following their difficult start to the title shootout at Croft, Brookes completed the podium to help close things up in the overall standings, the Australian moving up to second position, 11 points behind Tommy Hill.
Brookes's cause was further aided by a first corner retirement for Michael Laverty, the Relentless Suzuki rider losing the back-end of his machine to record a costly retirement. He is now behind both Brookes and Kiyonari in the title reckoning, 19 points off the lead with three races remaining.
Race one winner Michael Rutter was another to fail to finish, the BSB veteran crashing out of third position to all-but-end his chances of winning the 2010 title.
Hill, meanwhile, battled his way to fifth place behind Alastair Seeley after never looking entirely comfortable in the conditions, though he did show his mettle by fighting his way past a Dan Linfoot and Gary Mason.
Linfoot put in a superb charge to finish in sixth for Motorpoint Yamaha after Loris Baz crashed at turn one, while Mason ended his race in seventh after running as high as third at one stage.
Chris Walker, John Laverty and Peter Hickman completed the top ten in what was a race of attrition, just 18 riders reaching the chequered flag.