The Russian's best time of 1:30.819 was set with just two minutes remaining: HÃ¼lkenberg and Clos crossed the line soon after to put themselves within a tenth of the top spot, but ran out of time as they tried to find a fraction more on their first visit to the technical new circuit.
This morning's fastest man Luca Filippi continued in qualifying where he left off, setting the early running as the field enjoyed their first full dry laps and held on to the top spot as everyone returned to the pits for their second set of tires.
Any hope the Italian had of repeating the performance on his second set were soon dashed, however, when Lucas di Grassi and Roldan Rodriguez broke through as the temperature soared. With most of the field smashing their previous times as the clock ran down, pole position looked like it could belong to anyone.
With the smallest of mistakes the difference between success and failure it was Petrov who held his nerve for his second consecutive pole position, while the new champion will have to make do with a second row start, next to di Grassi and ahead of Davide Valsecchi, Rodriguez, Alberto Valerio and Pastor Maldonado.
Local fans were disappointed by the non-appearance of Alvaro Parente, who were expecting to see their hero around the top of the timesheets: the Portuguese driver was unable to set a time after suffering a gearbox problem, and will have to rely on the good graces of the race stewards to join the grid tomorrow.
With 15 drivers within a second of pole, and weather forecasts suggesting more of the same conditions tomorrow afternoon, the stage is set for open warfare as the championship contenders fight to bring back the team's title for their respective groups, while Clos sits between them and looks for his first score of the season.