Riewoldt left the game in the dying seconds of the first half after falling to the ground grimacing in pain and clutching his right hamstring in a marking contest.
He did not reappear in the second half, but his teammates dug deep to register a stunning 10.9 (69) to 4.17 (41) win that keeps the Saints' unbeaten start to the season intact.
The gritty second-half performance was worthy of the highest praise considering important defender Sam Fisher was absent until midway through the final term after suffering a knock to the head early in the third quarter.
St Kilda coach Ross Lyon was delighted at the resilience of his players in the face of such adversity.
"I thought it was a magnificent effort - everything was thrown at us, and we responded like good teams do," Lyon said.
"The merit of the four points under extreme adversity... was really valuable for the belief."
The defensively-minded Magpies came out determined to blunt the scoring power of the potent Saints attack and succeeded in a first half that produced just four goals to each side.
The Pies held a three-point lead at the main break, but failed to register a major in the second half as their diabolical kicking for goal robbed them of any chance at the premiership points.
Despite a clear numerical advantage, Collingwood couldn't match the spirit of Lyon's men who banged through the last six goals of the game to register the win.
Sam Gilbert was the leading possession winner on the ground, gathering 32 disposals playing mostly loose in defence with Jason Gram also prominent with 29. Steven Baker was outstanding with 28 touches while effectively negating Pies' danger man Leon Davis.
Fisher came back on to finish the game with 28 possessions and typified the courage of the Saints with his late effort to mark the ball while going back with the flight into traffic.
Luke Ball led Collingwood with 28 disposals against his old side, but he was also guilty of missing important set shots at goal. Dane Swan (26 possessions) and Sharrod Wellingham (25) were also important.
There was plenty of niggle in the at-times spiteful contest, which started with a free kick to Sharrod Wellingham after a melee before the first bounce that involved most players from both sides.
Collingwood coach Mick Malthouse dismissed the notion that his players might have thought the four points were in the bag once Riewoldt limped off and was mystified by his side's inaccuracy in front of the big sticks, which he said was 'just not good enough'.
"We practise enough; your guess is probably as good as mine," Malthouse replied when asked about the wayward display.
"It's the old cliché. A lot of things might change in life but one certainly doesn't - bad kicking is bad footy. You don't kick enough goals, you don't win games of football."
St Kilda 2.2 4.5 6.6 10.9 (69)
Collingwood 1.4 4.8 4.14 4.17 (41)
GOALS
St Kilda: Goddard 2, Montagna 2, Dal Santo, Milne, Gram, Schneider, Gardiner, Gwilt
Collingwood: Cloke, Didak, Sidebottom, Beams
BEST
St Kilda: Gram, Hayes, Gilbert, Baker, Dal Santo, Goddard
Collingwood: Swan, Cloke, O’Brien, Wellingham, Ball, Sidebottom
INJURIES
St Kilda: Riewoldt (hamstring), Fisher (concussion), Hayes (nose)
Collingwood: Cloke (ankle)
Reports: Nil
Umpires: Vozzo, Meredith, Ryan
Official crowd: 49, 669 at Docklands
The views in this story are those of the author and not necessarily those of the clubs or the AFL.
