Patric Niederhauser moved up to third in the GP3 standings with his second win of the season after being amongst those to benefit from a rain-induced red flag period.
A downpour at the start saw the race start behind the safety car, but with many still on slick tyres. Pole-sitter Daniel Abt led a train of cars in at the end of the first lap to switch to wets, while Conor Daly took the race lead behind the safety car.
With conditions worsening the decision was taken to suspend the race. It got going again, but with several more laps under the safety car despite the track seemingly drying quickly.
Once it got going, fifth-place starter Niederhauser passed Daly for the lead and stayed ahead to win by 0.6 seconds.
Behind Daly, Kevin Ceccon took third but subsequently had 30 seconds added to his time after not having his tyres fitted before the three-minute signal before the race.
That handed a first podium finish to his compatriot Giovanni Venturini in just his second weekend in the series. It was also the first points finish in GP3 for the Trident team.
Matias Laine took fourth ahead of fellow Finn Aaro Vainio, who started 13th due to a grid penalty handed to him for hitting Laine in the second Silverstone race. Tamas Pal Kiss was sixth.
Abt and championship leader Mitch Evans rejoined after pitting in 14th and 15th places but worked their way up the order to cross the line eighth and ninth. Ceccon's penalty promotes them to seventh and eighth, and sees Evans on the reverse grid pole for Sunday's race, with chief rival Vainio having now closed to just four points behind in the standings.
William Buller was classified ninth ahead of Tio Ellinas. The Cypriot recorded the fastest lap on the last lap as he passed Robert Cregan on his way to recovering from his back-row starting position after he was excluded from qualifying for a technical infringement.
Alex Brundle and Robert Visoiu were both excluded after the race. They had been guilty of the same offence as Ceccon, but were notified under the safety car. They served their stop/go penalties but did so under the safety car.
Antonio Felix da Costa's hopes of catching the championship leaders were dealt a blow when he broke a wheel and finished up in the gravel trap.
