Jason Plato took a second win at Donington Park to extend his championship lead over Fabrizio Giovanardi.
The Italian now trail the Seat driver by 25 points in the championship.
The near-flooded track meant the third race was run with the run into the Old Hairpin under permanent yellow flags. A small stream was running across the apex of the right-hander.
Colin Turkington was the first driver to splash through the water as he led on the first lap before being passed by Mike Jordan. Plato fought his way through the field from ninth, deftly taking Matt Neal by driving around the outside of the reigning champion at Redgate.
Plato then took Jordan for the lead at Old Hairpin but, fearing he would be penalised for the move, allowed Jordan to re-pass him. He had no trouble taking the lead back and stormed off to the win.
Neal then passed Jordan for second, the independent driver completing the podium. But Giovanardi once again struggled with malfunctioning windscreen wipers – vital in the thick spray – spun off, and finished 11th.
Having spent the earlier races slowly closing on Plato he has it all to do again.