Trainer Bryce Heys has refused to be drawn on Spieth's next assignment, preferring to let him get over his first stakes win at Randwick.
The lightly raced four-year-old missed the start of the Listed Tattersalls Lightning, but was well in front at the end of the 1100m, beating Kaepernick by three-quarters of a length.
Jay Ford kept his cool on the $3 favourite, much to the relief of Heys.
"Jay kept his cool," Heys said. "I thought he would got up the fence but he was patient and waited for the gap.
"I'm excited about where this horse goes next but I'll let him get over this first.
"We have a plan in place if he could win today and we will decide by the middle of the week but he will go to Melbourne."
Spieth is entered for the Group One Darley Classic on the 1200m straight course at Flemington on November 5 but there is also the option of the Group Two Linlithgow a week earlier over the same distance.
Ford said Spieth had played up in the starting stalls.
"He was sitting down and I was trying to get a barrier attendant to grab his tail and I was turning around asking him and next minute the gates were open," Ford said.
"He came out very awkwardly but he was able to recover.
"He is a serious horse on the way up and he is in for a good campaign."