The result was the worst he had ever suffered as a manager and immediately plunged his role at the club into doubt. After talks with the Morton directors, a parting of the ways became inevitable on Tuesday night.
"After that defeat on Saturday, Morton wouldn't be able to move on, I don't think, with me still in place," said Shiels yesterday. "It was a real sore one. I'm in the firing line, and that sort of thing has to be a manager's responsibility. The club had to be able to move forward, with season-tickets to sell for next year and so forth.
"I had to appreciate the club needed mental refurbishment, so I had to leave. With me still there, I think selling season tickets would have been more difficult."
Shiels, who had to rush off back to Northern Ireland for a funeral immediately after the Hamilton game, has since been left picking over a match which proved to be his abrupt downfall in Greenock.
"Saturday's game was a disaster," he said. "I was very embarrassed by it, it was hurtful. Oddly enough, at 2-1 down we had looked the likelier to score, but Hamilton hit us with bursts of goals.
"I asked myself, 'should I have set up any differently?' but we'd had three clean sheets in four games and had gone three wins, a draw and a loss in our last five. The Hamilton game just became an unbelievable situation.
"There is absolutely no excuse for what happened, but psychologically it is perhaps explainable to a degree. Hamilton were going for promotion and needed a load of goals, while Morton were already relegated. None of this excuses it one bit, but it explains it a little."
Shiels was further wounded by comments made by Paul Hartley, the Dundee manager, who said that such a scoreline as 10-2 "doesn't even happen in amateur football". Hartley, it has since been noted, played in and was sent off in Aberdeen's 9-0 defeat to Celtic in Glasgow in November, 2010.
At Morton there was a constant rumour about Shiels, who could not take his own No.2 with him to the club, not seeing eye-to-eye with certain backroom coaches whom he inherited at Cappielow.
"There have been certain issues going on at Morton which I don't want to speak about," he said. "I take the responsibility, and I've resigned, and I need to move on with my life. This experience will make me a better manager - I know it will. I want to - and I need to - get back to work in football.
"For the record, I'd love to see Morton one day in the Premiership - that was my goal until recently. I'd love to see it especially for the chairman [Douglas Rae] who has put so much into the club. But I just have to move on. It didn't work out for me and I feel really sorry about that."