Mitch Evans came from 10th on the grid to secure a shock feature race victory at a rain-affected Red Bull Ring, ahead of Campos team-mate Sean Gelael.
Italian Raffaele Marciello completed the podium in an utterly bizarre race.
Pierre Gasly had looked set for his first victory until he spun off as heavy rain engulfed the Austrian circuit. Team-mate Antonio Giovinazzi also missed out on a possible third win in a row when he was left stranded at the end of the pitlane.
The race was interrupted by two safety cars and a red flag, but it was a strategic call from Campos that ultimately secured a surprise one-two result.
Prema teammates battle it out at start
Sergey Sirotkin bogged down badly from his third GP2 pole and was swallwed up by the Prema duo of Giovinazzi and Gasly off the line, while there was contact at the rear of the field as Sergio Canamasas vaulted over Gustav Malja and Nabil Jeffri into retirement.
At the front, Gasly pumped in a series of fastest laps as he hounded Giovinazzi. The Frenchman wasted no time in making his move and lunged into the lead under braking into turn one.
The two team-mates brilliantly ran side-by-side on the run up to turn three with Gasly making it stick on acceleration. He then proceeded to streak away at the front, but heavy rain was on its way.
Behind the top two, the Russian Time of Artem Markelov was making progress, having lost ground at the start. The erstwhile championship leader made amends by pulling off consecutive overtakes on Oliver Rowland and Alex Lynn.
Team-mate Raffaele Marciello gained a place at the start and ran steadily behind compatriot Luca Ghiotto in fifth. Marciello bided his time behind the Trident car before completing a bold move into turn four as the pair closed on Sirotkin ahead.
Rain hits circuit, Gasly out
Ghiotto began to struggle as the rain began at the top of the circuit and fell into the clutches of Norman Nato. Next time around, turn two was greeted with monsoon-like conditions as lap-times dropped by six seconds.
With conditions getting worse by the lap, Gasly soon took himself out of contention with an agonising spin into the turn four gravel trap. The winless run continued as the hapless Prema driver sat beached and out of the race; Giovinazzi inherited the lead behind the safety car.
The bulk of the field restarting on slicks on a part-dry, part-wet circuit, inevitable chaos ensued as Giovinazzi and Marciello switched back and forth for the lead no less than four times, the pair barely keeping their cars on the road.
Sirotkin kept the leaders in sight but also had to defend heavily from Ghiotto, Rowland and Evans, who had pitted earlier along with team-mate Sean Gelael.
The top four were separated by less than three seconds and had to masterly navigate the stricken Carlin of Marvin Kirchhöfer in the middle of turn two.
Cue a second safety car phase and the mandatory pit-stops. Marciello got ahead of Giovinazzi but it was still Evans who was the de facto leader. Markelov’s promising race came to an abrupt end when he crashed on pit exit, prompting race organisers to throw a red flag.
Six lap sprint to the end
Giovinazzi’s race unravelled spectacularly when he got caught behind the stalled ART of René Binder – subbing for the banned Nobuharu Matsushita. Giovinazzi, stationery at the end of the pitlane went a lap down to new race leaders Evans and Gelael.
Safety car in: Evans, who qualified 10th, skipped out to an comfortable lead ahead Gelael but further back, Marciello was making inroads. The Italian, on new tyres got past Jimmy Eriksson and Ghiotto to run third with six to go.
Eriksson and Rowland battled hard for fifth place for the remaining five laps with the Briton having made his way past round the outside of turn two. Eriksson, vice-champion in GP3 in 2015, fought back and with the use of DRS, breezed back past on the penultimate lap to claim valubale points for Arden.
Out front, Evans was never challenged since the restart and the Kiwi led Geleal in a Campos one-two as the flag fell. Marciello completed the podium ahead of Ghiotto, Eriksson, Rowland and Nato.
Sirotkin claimed eighth place and with it, reverse grid pole for Sunday’s sprint race.
