Midway through the session, ART's Stoffel Vandoorne took control of GP2 practice at Sochi on Friday - and once he was out in front he proved to be totally uncatchable by the rest of the field, who were instead left scrapping over the dubious honour of who would be the best of the rest behind the McLaren F1 test and reserve driver.

CLICK: Full GP2 practice session times from Sochi Autodrom.

The 3.634-mile, 19-corner street circuit was still somewhat the worse for wear following extensive clean-up efforts for a major diesel spill through turns 6, 7, 8, 9 and 10 earlier in the day that had caused a half hour delay to the start of F1 Free Practice 1. The lack of running in FP1 has also resulted in a severe lack of rubber being laid down on the circuit by the F1 cars. Another cause for concern among the teams and drivers were the heavy clouds approaching Sochi threatening to further wet the track with outbreaks of rain during the 45-minute session.

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While most drivers were quick to head out onto the track to check the conditions, only half the field initially opted to stay out and complete a fully timed lap with DAMS' Alex Lynn setting the early pace with a 1:50.585s eight tenths ahead of Trident's Raffaelle Marciello. Lynn's team mate Pierre Gasly took up third spot ahead of the Rapax in the hands of Sergey Sirotkin.

The rest of the field were soon back out to join the fray, and Carlin's Dean Stoneman briefly jumped to the top with a new benchmark of 1:50.334s for the others to aim at, only to have it immediately trashed first by championship leader Stoffel Vandoorne and then by Marciello who moved the goalposts to 1:47.991s. Lynn and Gasly's next efforts weren't enough to go to the top and they had to be satisfied with injecting themselves into second and third place behind Marciello.

New efforts from Sirotkin and Campos Racing's Arthur Pic demoted the DAMS pair down two places. Pic's team mate Rio Haryanto went even better and cut the gap to Marciello to under four tenths of a second, but it was left to Lynn to pull out something special to enable him to go to the top of the timing screens by half a second with a lap of 1:47.483s. Predictably however it was Vandoorne who was next to show his teeth and rise to the challenge to go top; Gasly's response was an improvement but still a worrying four and a half tenths off the Belgian's pace even before Vandoorne then put in a thumping new effort of 1:46.117s to put himself over a second clear of the rest of the field after 20 minutes.

Russian Time's Mitch Evans had been one of the last drivers to embark on his first set of timed laps, and his wait had enabled the track conditions to improve somewhat so that he was now able to get to within half a second of Vandoorne's fearsome benchmark. Haryanto went even better and posted a lap of 1:46.276s suggesting that the battle for the top spot might not be quite done yet, even as the drivers made their mid-session return to pit lane for discussions with their teams and set-up changes to their cars.

When battle recommenced, Vandoorne continued to lead the way, once again extending his lead at the top to almost a full second with a new lap of 1:45.326s. Evans' prompt response was only good enough for second place a tenth ahead of Haryanto, and the Indonesian ace made his own riposte to leapfrog the Kiwi with an improved lap of 1:46.099s. That was still 0.773s off Vandoorne at the front, who seemed to be working on a completely different track from the rest of his rivals.

With less than five minutes remaining on the clock, the drivers began their final runs. First blood went to Pic who moved into second place just ahead of his team mate Haryanto, but he was still seven tenths away from the leader whose time appeared utterly impervious from attack. His point well and truly made, Vandoorne ended the session a few minutes early and was able to watch the final runs from the pit wall. However with increasing moisture in the air it soon became evident that there was no further room for improvement at the top of the timesheets, although the actual rain considerately held off until just moments after the chequered flag had declared the end of the session.

Behind Vandoorne, Pic and Haryanto, Evans held on to fourth from the DAMS duo Lynn and Gasly with Sirotkin in seventh ahead of Racing Engineering's Alexander Rossi who is making his return to GP2 this week after two outings in Formula One in the interim at Singapore and Japan. Marciello ended practice in ninth place just ahead of Vandoorne's ART team mate Nobuharu Matsushita in tenth.

Despite the state of the track there were only minor run-offs and lock-ups at various points on the circuit during the session for the likes of Lynn, Sirotkin, Stoneman and Trident's Johnny Cecotto Jr., together with a relatively harmless early 180-degree spin for Rossi early in the proceedings.

After missing the last outing at Monza in favour of a one-off ride for GP3 contender Patric Niederhauser, Nathanael Berthon was back with Lazarus and ended practice in 12th place. The team announced this week that it was pulling out of the GP2 Series at the end of the season and that their place on the grid would be taken by Prema Motorsport.

With Daniel de Jong still recuperating from spinal injuries suffered in a nasty crash at Spa-Francorchamps at the end of August, Nicholas Latifi returned to MP Motorsport alongside Rene Binder. The pair ended up adjacent on the timing screens, with Binder just getting the better run in 15th once spot ahead of Latifi in 16th.

After fielding just one car for Simon Trummer in the last round at Monza, the Hilmer Motorsport team will be missing altogether from this weekend's round. The squad posted on Twitter that "Unfortunately, our team will not be in Sochi this weekend, but we will keep on fighting to be back in Bahrain."

The remaining teams and drivers will be back in action again this afternoon for qualifying which gets underway at 4pm local time (2pm BST). That will set the starting line-up for the 28-lap feature race which gets underway on Saturday afternoon at 4.40pm (2.40pm BST), while the 21-lap sprint event will get the green flag at 11.05am (9.05am) on Sunday morning.

The GP3 drivers are also in action this weekend, starting with their sole practice session later today at 5pm (3pm BST) and qualifying on Saturday morning at 9.30am (7.30am BST). The 20-lap race 1 is scheduled for later on Saturday at 1.30pm (11.30am BST) and the shorter 15-lap race 2 will be on Sunday morning at 10am (8am BST).

See full GP2 practice session times from Sochi Autodrom.