The South Australian, who won four heats and came second in the fifth to WA champion Daniel Winchester, finished the heats on 14 out of 15 points, same as Victorian Ty Proctor, but Parker proved too strong in the final.
Proctor came second, ahead of Winchester who finished the heats on 13 points.
Resident Italian rider Paco Castagna won the B-final, with Blake Russell second and Trevor Williams third.
The meeting also included the Gordon Rowland Memorial Shield for the under-16 125cc competitors.
Reigning WA champion Matt Marson won all of his heats before taking out the final ahead of Declan Knowles and Kobee Ziedas.
Sheldon Gill won the B-grade final.