The Eagles led by 11 points early in the last quarter of Saturday's match, but three final-term goals to Mason Wood helped lift St Kilda to the 12.10 (82) to 10.8 (68) victory.
Reid faces a nervous wait after slinging Saints youngster Darcy Wilson to the ground in the third quarter.
The force and slinging nature of the tackle resulted in the back of Wilson's head hitting the turf.
Darcy Wilson received a free kick following this Harley Reid tackle.— AFL (@AFL) #AFLEaglesSaints pic.twitter.com/Rhs2htAPrsJune 1, 2024
Wilson went off to be assessed for concussion, but was later cleared to return.
If Reid is suspended, the prized No.1 draft pick will be ineligible to win the Rising Star award.
With raging hot favourite Reid in danger of being suspended and Western Bulldogs forward Sam Darcy now ineligible after copping a two-match ban, the award could be thrown wide open.
Reid looked set to be the difference in Saturday's match after a 17-disposal, seven-clearance first half, but he was restricted to just three possessions in the second half after being tightly tagged by Marcus Windhager.
St Kilda's win came at a cost, with star forward Max King subbed off at three-quarter-time with a knee injury.
West Coast veteran Jamie Cripps and goalsneak Liam Ryan kicked three goals apiece, while Tom Barrass and Jeremy McGovern were exceptional in defence.
Wood finished with a game-high four goals to go with 22 disposals.
West Coast suffered a huge late blow when Coleman Medal fancy Jake Waterman withdrew with a shoulder injury.
It came on the back of star midfielder Tim Kelly (hip) pulling out a day earlier.
The opening term was an error-riddled affair, with St Kilda particularly guilty of butchering the ball in a quarter when their disposal efficiency was a woeful 52.1 per cent.
An early goal to King was St Kilda's only joy for the term, with Andrew Gaff and Jack Darling hitting the scoreboard for West Coast to give the home team a nine-point lead.
Reid amassed 13 disposals and six clearances during a monumental second-quarter display.
St Kilda hit the lead early in the quarter, but Reid's heroics ensured West Coast entered the half-time break with a 14-point lead.
Saints coach Ross Lyon would have been fuming at the long break after the Eagles scored goals through Cripps and Ryan in the final 30 seconds of the half.
Lyon sent Windhager to tag Reid in the third quarter, and the move worked a treat as the Saints kicked three unanswered goals to snatch the lead.
Two goals to Ryan within the space of a minute ensured West Coast headed to the final change with a five-point edge, but St Kilda completely dominated the last quarter.
