Kiwi Scott McLaughlin has set the fastest time in the opening practice session of the Sydney 400 championship finale.

The departing Volvo driver set a time of 1:27.8s to head off Holden Racing Team's James Courtney and championship contender Jamie Whincup.

Championship leader Shane van Gisbergen sat atop the standings for the majority of the session but was eclipsed as time expired and ended up with the fourth fastest time of the session.

He carries a 191-point championship lead over Red Bull Racing teammate Whincup heading into the final two races of the weekend and showed that he will be hard to beat on a track where he's enjoyed tremendous success in recent years.

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"The track is very slippery," van Gisbergen said afterwards. "The rubber will go down and we will go quicker and quicker.

"First session the car was quite nice but we just need to chase the track now."

There were dramas for a number of cars during the session. Reigning series champion Mark Winterbottom suffered an electrical failure on his first out-lap and had to coast back to pit lane. He remained there for nearly half of the 40 minute session as his team rectified the problem. They sent him back out and he was able to post some times but the issues continue to plague car #1 throughout the session.

Two of the Nissan Altimas - Dale Wood and Todd Kelly's cars - had oil leaks thanks to overfilling while Chaz Mostert ran down the escape road after locking up.

Championship leader van Gisbergen had a massive moment on a flying lap as he caught an idling James Moffat in an awkward part of the track. The Kiwi was lucky to avoid contact with either the Volvo or the wall, which could have spelled disaster. Thankfully it only cost him with what looked like the fastest lap of the session at that point.