The Magpies started well, with a tough quarter and a half that saw neither team kick consecutive goals, but then the Saints took control, kicking 12 of the next 14 to finish the game as a contest in the third term.
The Pies had won 18 of their last 19 second terms, but looked tired and battle-weary after a long season after kicking the first goal of that term, and the final score of 17.4 (106) to 9.18 (72) showed the fatigue.
Riewoldt was simply unstoppable – he finished with five goals and 15 marks as he cut up youngster Nathan Brown before Nick Maxwell was swung on to him in the last term.
Both teams made changes before the bounce – Collingwood skipper Scott Burns and Simon Prestigiacomo were replaced by Rhys Shaw and Shane Wakelin, while the Saints made the expected change, and brought in Jarryd Allen to replace ace Luke Ball.
Shaw was dynamic for the Pies, linking play beautifully through the midfield, while John Anthony ended with three goals after being a good target forward early. Scott Pendlebury and Dane Swan were good through the middle, while Leon Davis worked hard when the game was on the line.
Josh Fraser battled hard in the ruck, but lowered his colours to Steven King, while Harry O'Brien did well in an overworked defence.
For the Saints, Robert Harvey was stellar in the first half when the game was there to be won, Justin Koschitzke improved as the game wore on, Stephen Milne kicked three, Raphael Clarke swept the backline in one of his better games for the club and Sam Fisher blanketed Paul Medhurst beautifully.
It was a comedy of errors early as the pressure from both sides told, but eventually the first goal arrived after nine minutes, with Justin Koschitzke marking a Harvey pass at 40. The teams then swapped goals for the remainder of the term and the Saints led by three points at quarter time after seven lead changes.
The Pies started the second term in promising fashion, with Tyson Goldsack knocking down a handball at the top of the 50, and following it up to gather and kick truly. But that was the end of the joy for Collingwood for the quarter, as the Saints broke the run of alternating goals and booted four straight, while the Pies added just six behinds, and the Saints led by 14 points at the long break.
The third term was more of the same, with Collingwood's only goal coming from the until-then unsighted Travis Cloke, while the Saints piled on six to lead by 40 points at the last change.
Youngster John McCarthy kicked the first of the last, then Paul Medhurst added his 50th for the year and when Brown kicked the next, it was the first time for the night that the Pies had scored consecutive goals. Marty Clarke kicked the Pies last.
Next week, the Saints take on Hawthorn on Saturday night for the right to play in the grand final.
St Kilda 4.1 8.1 14.2 17.4 (106)
Collingwood 3.4 4.11 5.16 9.18 (72)
GOALS
St Kilda: Riewoldt 5, Milne 3, Koschitzke 3, Gram 2, Dal Santo, Gwilt, McQualter, Schneider.
Collingwood: Anthony, Brown, Goldsack, Clarke, Cloke, Lockyer, McCarthy, Medhurst, Swan.
BEST
St Kilda: Riewoldt, Dal Santo, Harvey, Clarke, Gilbert, Montagna, Fisher, Gram, Blake.
Collingwood: Swan, Fraser, Davis, O'Bree, Pendlebury, R Shaw.
INJURIES
St Kilda: Ball (hamstring) replaced in selected side by Allen, Allen (hip).
Collingwood: Burns (calf) replaced in selected side by R Shaw, Prestigiacomo replaced in selected side by Wakelin.
Reports: St Kilda: Koschitzke reported for rough conduct on Wakelin by umpire Kennedy
Umpires: Kennedy, Rosebury, McLaren
Official crowd: 76,707 at MCG
