Duncan displayed class and poise with 20 disposals and 13 marks for the afternoon while Jimmy Bartel was awarded seven votes from Chris Scott and Alan Richardson for his 32-disposal effort.
Mathew Stokes continued his brilliant form and was awarded five votes from the coaches while Steven Motlop was back to his flashy best, collecting four votes for his 29 disposals, a season high.
Dawson Simpson was also awarded two votes for his 52 hit-out domination in the ruck contest.
Geelong vs St Kilda
8 Duncan (Geel)
7 Bartel (Geel)
5 Stokes (Geel)
4 Motlop (Geel)
2 Hawkins (Geel)
2 Simpson (Geel)
1 Mackie (Geel)
1 Taylor (Geel)
Cats leaderboard
Joel Selwood 38
Steve Johnson 29
Jimmy Bartel 28
Tom Hawkins 24
Mitch Duncan 20
Mathew Stokes 19
Harry Taylor 18
Cam Guthrie 12
James Kelly 9
Tom Lonergan 7
Andrew Mackie 6
Steven Motlop 4
George Horlin-Smith 3
Dawson Simpson 2
Corey Enright 2
Jared Rivers 2
Jordan Murdoch 2
Hamish McIntosh 1
Travis Varcoe 1
