The Power's 16.11 (107) to 9.16 (70) victory over Collingwood at the MCG - a win highlighted by Warren Tredrea's best-field effort and another superb defensive performance by Chad Cornes - means Port cannot finish lower than third following next week's final home and away round.
But provided they beat local rivals Adelaide next week, Port will finish in the top two for the third successive season and again host two finals at AAMI Stadium.
However after watching his team thrash the Magpies, Williams says his side is better prepared for this year's finals series than it was in 2002 and 2003 when its good work in finishing on top of the ladder was offset in both years by surprise first-up losses at home in the finals.
Williams said the fact his team had been forced to overcome so many injuries to key players this season had made the team mentally tougher.
"No doubt we are a better team because of the closeness of the group and they want to play for each other," Williams said.
"We are not satisfied with how we've gone (in past finals series), the players know we have let ourselves and our public down and we are going to play harder footy (in this year's finals).
"We have been disappointing in finals in the past but now we get to have another crack at it."
"We have lost significant players during the season but we have showed a lot of character to overcome that and that is the stuff finals are won on."
With Tredrea and Cornes in such devastating form, Port was untroubled by the Magpies after quarter-time on Friday night.
After trailing by seven points at the first change, Port put the match beyond doubt with a seven goal to one second quarter with Tredrea and Byron Pickett each kicking two goals in the second term onslaught.
Tredrea, who had been in doubt for the match all week with a shoulder injury sustained against the Bulldogs in Darwin last week, was best-afield with 13 marks and three goals while Cornes helped himself to 24 possessions and eight marks.
Kane Cornes finished the match with a game-high 30 touches, including 21 in the first half, while Brendon Lade and Dean Brogan rucked superbly to give the Port runners constant first use of the ball.
And as a result the likes of Peter Burgoyne (24 touches), Josh Carr (22) and Roger James (23) helped themselves to plenty of touches while Matthew Bishop was superb in defence in keeping the Magpies' premier forward in Chris Tarrant goalless.
The win was just Port's sixth in 19 matches at the MCG but significantly their fourth in the past eight matches with Williams declaring his team was not concerned about its ability to play on the ground where premierships are decided in September.
"We haven’t got our MCG (winning) percentage where we would like it but it's moving in the right direction," Williams said.
Collingwood: 3.3 4.8 5.12 9.16 (70)
Port Adelaide: 2.2 9.7 13.10 16.11 (107)
Goals: Collingwood: Lonie 3, Burns 2, Lockyer, Fraser, McGough, Johnson
Port: Tredrea 3, Wanganeen 2, Pickett 2, Lade 2, Thurstans 2, Schofield, Carr, Brogan, Wilson, Cochrane
Best: Collingwood: Licuria, Woewodin, Lonie, Rowe, Cole, Burns
Port: Tredrea, C Cornes, Lade, K Cornes, Carr, P Burgoyne, Bishop, Wanganeen, James
Injuries: Collingwood: Prestigiacomo (shoulder) replaced in selected side by Williams
Port: Nil
Reports: Nil
Umpires: Vozzo, Kennedy, Woodcock
Crowd: 27,226 at MCG
