A September bolter has combined with a flaky Port Adelaide to turn the AFL finals series on its head for the second successive year.

Injury-plagued Sydney - even coach Paul Roos was on crutches - staged the upset of the season when it beat the premiership favourite Power by two goals at AAMI Stadium.

The 15.10 (100) to 13.10 (88) qualifying final result also strengthened Port's reputation as a finals choker.

This time last year, Collingwood went into the finals with no form and also upset minor premier Port at home in a qualifying final.

Now, the Swans have ruined the possible dream preliminary final matchups of a Port versus Adelaide Showdown and traditional rivals Collingwood and Essendon at the MCG.

But Port coach Mark Williams insisted he had not lost faith.

"If I believed the evidence of the second quarter or the first half was a true indication of how they will be or are I'd be very disappointed," Williams said.

"I really believe in the guys, I'm a person that thinks that it doesn't always run perfectly for you."

While Collingwood and Sydney have a week off, Brisbane will host Adelaide on Friday night in one semi-final and Port will be at home to Essendon on Saturday night in the other semi.

It will be the first time in VFL/AFL history that Melbourne has not hosted a game during a finals weekend.

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