Jason Plato held off a charging Fabrizio Giovanardi to win the second British Touring Car Championship race of the day at Silverstone.
Plato passed his polesitting RML Chevrolet team-mate Mat Jackson at Copse on lap eight and opened up a one-second lead.
However, with rain falling at the half-distance mark and becoming heavier as the race progressed, neither Chevy driver could match the pace of Giovanardi's Vauxhall, which closed in at a rate of around half a second per lap.
The Italian passed Jackson for second on lap 18 when the latter put two wheels on the grass at the exit of Brooklands and then reeled off a succession of quick laps to close the three-second gap to Plato.
His charge failed by less than a second, with Plato taking his third win of the season and the 49th of his BTCC career.
Jackson completed the podium, ahead of Colin Turkington's WSR BMW. Turkington's result means that his championship lead has been cut from 11 points to seven by Giovanardi.
Tom Chilton took the best finish for Arena Motorsport's Ford Focus after displaying supreme wet weather pace. His finishing spot came, however, only after he and James Nash (RML Chevrolet) made contact at Becketts on the last lap.
Andrew Jordan (Vauxhall) and Jonathan Adam (Motorbase BMW) were next up, while Johnny Herbert took his first BTCC points with eighth place.
It was a poor race for Matt Neal in the third of the Vauxhalls. He went off three times, firstly after contact from Rob Collard (who had earlier been hit by Giovanardi while they battled for fifth place), and twice on his own once the rain came down.
Pos Driver Car Time
1. Jason Plato Chevrolet 24m00.312s
2. Fabrizio Giovanardi Vauxhall +0.771
3. Mat Jackson Chevrolet +3.181
4. Colin Turkington BMW +12.948
5. Tom Chilton Ford +13.678
6. Andrew Jordan Vauxhall +15.399
7. Jonathan Adam BMW +16.489
8. Johnny Herbert Honda +18.260
9. Rob Collard BMW +20.027
10. Paul O'Neill Honda +20.516
11. Harry Vaulkhard Chevrolet +22.239
12. Stephen Jelley BMW +23.791
13. Tom Onslow-Cole Ford +32.652
14. Anthony Reid BMW +36.766
15. Martyn Bell Honda +1 lap
16. David Pinkney Honda +1 lap
17. John George Honda +2 laps
James Nash Chevrolet 21 laps
Matt Neal Vauxhall 14 laps