A full-blown thunderstorm had barrelled over Singapore in the hour preceding the GP2 practice session on Friday. With the track still awash with standing water and a light rain still continuing as the green lights came on at the end of pit lane, it threatened to be a potentially expensive 30 minute session in store for the 26 drivers in their first outing on the street circuit in a GP2 car if they chose to be too adventurous or unwary.

Seeking to bounce back from a lacklustre Monza in order to clinch the GP2 team championship title, Lotus GP's James Calado and Esteban Guti?rrez were the first men out on the track. Meanwhile Barwa Addax's Jake Rosenzweig was the first driver to take to a run-off during the session at turn 8, and fortunately he was quickly able to get the car back out onto the circuit. The rest of the field were being notably cautious in the unknown, treacherous conditions and making sure they put safety first at this early stage.

It was Trident's Stephane Richelmi who set the best of the early times with a 2:24.520s which was soon pipped by Johnny Cecotto Jr. in the other Barwa Addax, Stefano Coletti in his second weekend with Rapax and then Nathana?l Berthon in the Racing Engineering car, as the wet tyres did their job by shifting water off the race line and providing more grip with every passing minute. On the next set of runs, Guti?rrez went top with a lap of 2:19.263s: that was beaten a minute later by Cecotto's latest response of 2:18.543s, and Guti?rrez responded in turn with a new effort of 2:17.784s.

Just ahead of the midway point of the session, the top of the timesheet was overtaken by a new wave of challengers led by Coloni's Luca Filippi, whose 2:17.243s was just 0.051s ahead of Fabio Leimer in the second Racing Engineering car. James Calado also nipped in front of Guti?rrez' time as yellow flags came out for a spin by Richelmi at the bridge that thwarted what had looked to be a fast lap for Coletti.

Just before the 20 minute mark, Cecotto returned to the top of the timesheets with a lap of 2:16.360s almost nine tenths faster than Filippi and Leimer who were both taking a pause in the pit lane for some set-up adjustments. That gave Carlin's Rio Haryanto - along with Felipe Nasr (DAMS) one of only two drivers to have raced before in Singapore in any series - the opportunity to briefly go second with a lap of 2:17.222.

A renewed push from Calado then put Lotus GP top with an impressive new benchmark time of 2:15.335s, and Guti?rrez briefly slipped into second place in the standings 0.186s behind his rookie team mate before then peeling off a second from the top time to post an effort of 2:14.339s despite encountering some traffic along the way and potentially improving his time through a section of the track showing waved yellows for a spin off by Caterham's Ricardo Teixeira.

The continued presence of yellows, together with a track that had by now got as good as it was going to at this stage of the day, meant that Guti?rrez' time would not be bested before the chequered flag came out, although Fabio Leimer closed up to within a third of a second of the Mexican's time to finish second in the timings, with Coletti also managing to just pip Calado for third place.

Notably, the two men at the centre of the GP2 championship battle - DAMS' Davide Valsecchi and Arden's Luiz Razia - barely featured during the session, perhaps preferring to play things ultra safe rather than to risk damaging their cars purely for practice session bragging rights. Valsecchi only briefly troubled the lower regions of the top ten before ending up in 14th place with a lap of 2:16.510s over two seconds off Guti?rrez' time at the top, while Razia was even further back in 20th place with a lap of 2:17.524s, over a second off Valsecchi.

The all-important GP2 qualifying will take place at 8pm local time (1pm BST) between Friday's free practice sessions for the F1 cars, with drivers doubtless hoping that conditions will have dried up by the time they have to brave the floodlights.

Both races will take place in the late afternoon daylight: the 34-lap feature event takes place on Saturday at 4pm local time (9am BST) while the 24-lap sprint race on Sunday is at 4.10pm local time (9.10am BST.) Thunderstorms are possible at any point throughout the weekend, which could make things very interesting indeed.

All sessions are due to be broadcast live in the UK on Sky Sports F1.

Full practice session times available.