Rain played a big part in GP2 qualifying in Monaco, with the rain that had earlier plagued F1 Free Practice 2 returning for an encore performance just as the cars headed out on track to set their flying laps.
In a staggered two-part qualifying, Trident's Raffaele Marciello proved the class act in the early part of the proceedings. However it was Racing Engineering's Alexander Rossi who got the best of improving conditions late in the session allowing him to claim pole position for only the second time in his GP2 Series career, as Stoffel Vandoorne's unprecedented run of qualifying success was finally brought to an end.
CLICK: Full GP2 qualifying times from Monaco
Because of the problem with congestion on the 2.075-mile, 19-turn street circuit leading to traffic jams ruining flying laps, Thursday's qualifying at Monaco was organised into two 16-minute sessions, the first comprising the 13 cars bearing odd numbers and the second for their even-numbered counterparts, the order having been determined by a random draw held during the morning and which ultimately proved crucial to the winning of pole position.
The track was still damp from the soaking it had taken during F1 afternoon practice as the GP2 cars streamed out of pit lane, and the persistent light rain soon started to pick up again meaning that those drivers that had been out on supersoft slicks expecting the track to continue developing a dry line ended up diving straight back into pit lane again for an urgent set of wet weather tyres instead. Marciello however went for the contrary approach and stayed out long enough to put in a banker lap of 1:45.404s almost a second faster than Racing Engineering's Jordan King and Carlin's Julian Leal.
Despite the steadily worsening conditions, Richie Stanaway soon took a second out of that time to go top with a lap of 1:44.493s to which Marciello instantly responded with a new benchmark time of 1:43.434s. The wet weather tyres were now coming into their own, and DAMS' Pierre Gasly leapt to the top with a lap of 1:41895s, half a second clear of Stoffel Vandoone. Vandoorne improved to 1:41.124s with his next lap but that was almost immediately bettered by Marciello who came back and responded with a time of 1:40.960s.
Given the tricky conditions for the session it was no surprise to see Hilmer Motorsport's Johnny Ceotto Jr. and Lazarus' Zoël Amberg both go down the run-off at Mirabeau during the short session, and Stanaway's early pace was also blunted when his front wing was damaged by light contact with the barriers.
Mindful that his time - while head and shoulders the best for his group - could still be beaten by the cars yet to follow in the second part of qualifying, Marciello wasn't satisfied with his time and managed to take another six tenths off, pushing so hard in the process that he then nearly lost it into the barrier at Massenet. No one else had a chance to respond to Marciello's time as there were yellows flags out at Mirabeau where Daniel de Jong had slid his MP Motorsport car into the barriers, while Amberg aquaplaned off into a hard impact with the Armco at the exit of Tabac with enough force to detach one of the wheels from his car. Also struggling in the wet conditions were Mitch Evans (Russian Time) and Pierre Gasly, both of whom overshot Sainte Devote but managed to avoid hitting anything important in the process.
That meant Marciello's time of 1:40.357s was the target for the second group to beat. Vandoorne's record run of six consecutive pole positions had finally come to an end after he finished second in the group ahead of Leal, King, de Jong, Gasly and Stanaway with Amberg ending the day in eighth ahead of Evans and Rio Haryanto, although the Indonesian driver would subsequently be given a three-place grid penalty for failing to slow sufficiently under yellow flags in sector 2 during the session.
The rain was already starting to ease off by the time the second group headed out from pit lane. This time everyone was on wet weather tyres and the rooster tail thrown up by Alexander Rossi's Racing Engineering car was testament to just how wet the track still was, with further evidence soon provided by Nick Yelloly who was the first to run off at Mirabeau in the Hilmer Motorsports car.
Rossi was the first driver to set a competitive time with a lap of 1:45.609s before he too took an impromptu rain check at Mirabeau which was fast becoming the incident black spot of the afternoon. Alex Lynn was up into second place in the DAMS ahead of Sergey Sirotkin (Rapax) and Nathaneal Berthon (Lazarus) but they were all quickly eclipsed by the next effort by ART's Nobuharu Matsushita who logged in at 1:43.482s
However Rossi was clearly in another class and his next lap of 1:41.046s put him back on top, seven tenths faster than Carlin's Marco Sorensen. With the rain now completely stopped there was a sense of inevitability when the American finally succeeded in bettering Marciello's first group target time with a scorching effort of 1:39.242s to put him two seconds clear of the others his own group. Just to put the matter beyond doubt, he then reduced the time still further 1:38.776s.
Those extra tenths proved to be much needed, as morning pacesetter Arthur Pic made a mid-session improvement to 1:39.006 for Campos Racing to go into second ahead of Lynn, Sirotkin and Matsushita, with Sorensen up to sixth after surviving a scary moment where his car was briefly launched into the air over the kerbs through the Swimming Pool.
Sunshine broke out just in time to allow the drivers to post a final late burst of improved times. Rossi made the most of it and ultimately pushed his provisional pole time all the way down to 1:37.019s with his final run, while Pic tried to stay with him but ended up finishing almost six tenths of a second further back. Sirotkin managed to pick up an extra place to end the group session in third place, while late bids from Yelloly and MP Motorsport's Sergio Canamasas saw them take over fourth and fifth positions, demoting Matsushita to sixth ahead of Russian Time's Arkem Markelov and Campos Racing's Andre Negrao. Barcelona sprint race winner Alex Lynn ended up badly missing out in ninth just ahead of earlier high flier Sorensen.
Thanks to running in the group with significantly better conditions by the end, Rossi's time was the fastest of anyone in the staggered qualifying session and he was duly rewarded with pole position. Marciello will start from second place alongside him on the front row of the grid as reward for being fastest in the first group.
The rest of the cars effectively line-up on the grid behind their 'group leader', meaning that Pic will start in third place alongside Vandoorne on the second row, and Sirotkin picks up fifth place with Leal next to him on row three. The top eight on the grid are rounded out by Canamasas and King.
The GP2 field will have the place all to itself on Friday while F1 sleeps in and takes the day off. By contrast the feeder series will be all-business with the start of the 42-lap feature race 1 set for 11.15am local time (10.15am BST), while the shorter 30-lap sprint race 2 will be held on Saturday afternoon at 4.10pm (3.10pm BST) following the conclusion of F1 qualifying.
See full GP2 qualifying times from Monaco