Cam Waters has gapped the field in final practice at the Penrite Oil Sandown SuperSprint.
Top spot was traded several times in the closing minutes, and Waters proved quickest of all.
Waters, who won the 2017 Sandown 500, was 0.33s clear of closest rival Chaz Mostert.
Will Brown impressed to third ahead of Shane van Gisbergen, Andre Heimgartner and Scott Pye.
The balance of the field rolled out on wet tyres before the sun broke through the clouds.
Drivers quickly reverted to Super Soft dry tyres, with a drying line emerging.
Will Davison set the first flyer on a 1:13.184s, before van Gisbergen lowered it to a 1:12.409s.
David Reynolds went quicker again, before Davison was first into the 1:11s.
Heimgartner pushed the marker to a 1:11.357s once drivers began to find tyre temperature.
Waters shot to the top on a 1:10.833s, before Mostert made the most of warm tyres to clock a 1:10.611s.
Davison’s 1:10.135s was blown out of the water by Waters’ 1:09.732s, before he improved to a 1:09.184s.
Several drivers hit trouble at the Turn 2-3-4 complex; notably, Broc Feeney was handed a bad sportsmanship flag.
Mostert also picked up mud and grass when he surfed through the infield, as did Jack Smith.
Mud and grass was flung onto the track, albeit off the racing line through Turns 3 and 4.
“Wasn’t wet, wasn’t dry,” Davison, who ended up seventh, said.
“It was like a mud pit out there.
“The last two laps, the track dried up to make a gain.”
Mostert added: “Super tricky.
“You’ve got to go to walking speed at the entry.
“You’ve got to take the speed off going across the grass because you can damage the car.”
Cars will return for three-part ARMOR ALL Qualifying at 12:50pm local time.
Qualifying will feature a Top Ten Shootout, which will set the first five rows of the grid for Race 24.
The 36-lap Race 24 will commence at 4:45pm.