Ridley was substituted out with a corked hip before the Bombers capitulated during the third quarter of the 17.6 (108) to 8.7 (55) loss at Marvel Stadium on Saturday.
The Saints piled on seven goals to one during the decisive period, including three majors to skipper Jack Steele, as Essendon failed to fire a shot in one of the most important moments of their season so far.
It led to a third consecutive defeat for Brad Scott's side and sixth in their past eight games, leaving them in a precarious position in a hotly contested race for finals spots.
Sitting third at the end of the bye rounds, Essendon could finish this weekend out of the top eight with four home-and-away matches left to play.
Nasaiah Wanganeen-Milera starred for St Kilda, who are out of finals contention but have won three of their past four games in a late-season purple patch.
Dashing playmaker Wanganeen-Milera had 30 disposals and six score involvements at half-back, and capped off a fine display with his first goal of the season.
Cooper Sharman kicked three goals and had 10 marks in a career-best performance, while Jack Sinclair (28 disposals), Riley Bonner (22) and veteran Zak Jones (22) were all busy.
Essendon coach Brad Scott faces a tough task to get his side into the AFL top eight. (Rob Prezioso/AAP PHOTOS)
Skipper Steele (21 touches) and ruckman Rowan Marshall (27 disposals, eight clearances) led from the front.
Anthony Caminiti (three) and Tim Membrey (two) also kicked multiple goals as St Kilda racked up their second-highest score of the season.
The Saints' conversion rate - 23 scores from 43 forward entries - and accuracy were superb, highlighted by Owens, Membrey and Caminiti all nailing goals from deep in the same pocket.
Essendon captain Zach Merrett (24 disposals, one goal) never stopped trying in a well-beaten side, while Dylan Shiel kicked two goals.
Resplendent in revived "candy stripes" jumpers for the club's retro round theme, the Saints produced a hot start and led 5.1 to 2.3 at quarter-time.
They repeatedly poked holes in Essendon's defensive structures and took seven marks to two inside 50m in the opening term.
Three goals in as many minutes briefly gave the Bombers the lead midway through the second quarter but St Kilda steadied and took a nine-point advantage to the main break.
Essendon's pressure dropped away during the crucial third quarter as St Kilda piled on the first six goals of the term and took a stranglehold on the contest.
In a telling statistic, the Saints finished with a massive tally of 133 uncontested marks while winning the contested mark count 16-5.
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