Sheridan opened the scoring when he glanced home Danny Racchi’s pin-point delivery after 26 minutes and James Fowler doubled the hosts’ lead 12 minutes into the second half.
A wonderful individual effort from James Dayton on the hour mark added to St Mirren’s misery, and despite Paul McGowan’s deflected consolation the hosts held on to claim their second win of the season.
Gary Harkins returned to the Kilmarnock starting line-up as a replacement for the injured Borja Perez while Danny Lennon handed a starting berth to Gary Teale – meaning Graham Carey began the game on the bench.
Kenny McLean’s effort from distance sailed just over Kyle Letheren’s crossbar in the opening minute before the hosts replied in positive fashion.
Harkins’ shot was deflected wide by Jim Goodwin and Michael Nelson fizzed a low effort from the edge of the penalty area inches wide of Craig Samson’s right-hand post.
Both sides were demonstrating attacking intent in the opening stages of the match and Manuel Pascali breathed a sigh of relief when Letheren made a good stop from Lewis Guy after carelessly losing possession to McGowan.
The Kilmarnock defence were looking nervous and Guy again should have profited when Paul Dummett robbed Racchi and sent the striker through on goal – however he could not round Letheren and Steven Thompson sent the rebound well wide of the target.
Marc McAusland became the first player to pick up a yellow card, after 14 minutes, when he handled the ball under pressure from Sheridan.
Sheridan then notched his first goal since arriving from CSKA Sofia earlier in the month.
St Mirren were too complacent in bringing the ball out of defence and Harkins was quick to dispossess McGowan before feeding Racchi who swung over an inch-perfect cross for Sheridan to nod home from six yards.
A reckless lunge on Dayton earned David van Zanten the second booking of the match after 28 minutes.
After falling behind against the run of play, St Mirren responded in a positive fashion.
Dummett forced James Fowler into a crucial goal-line clearance before Letheren did well to gather Teale’s strike at the second attempt.
Lee Mair became the third visiting defender to earn a booking for a careless challenge on Liam Kelly a minute before the interval.
Both teams struggled to retain possession in a scrappy opening to the second half, with McGowan’s tame effort after 52 minutes the only notable attempt on goal.
Kelly floated a shot high over the bar as Kilmarnock responded at the other end and they were to double their lead after 57 minutes.
Racchi’s shot was deflected off the back of Sheridan and into the path of Fowler who rocketed a shot beyond the helpless Samson.
The confidence was suddenly flowing through the home side and the afternoon was to get even better for them on the hour mark as they added a third goal.
Dayton weaved his way past two defenders before blasting the ball high into the net from a tight angle.
St Mirren manager Lennon reacted by making a triple substitution with 25 minutes remaining, with Sam Parkin, Dougie Imrie and David Barron all introduced.
The visitors should have pulled a goal back after 71 minutes when Guy connected with McGowan’s cross but his effort rebounded off the bar before Parkin blazed well over.
Home boss Kenny Shiels made two changes as Chris Johnston and Rory McKenzie came on for Harkins and Dayton.
McGowan gave the large Saints travelling support some late hope when his deflected effort left Letheren flat-footed and found the bottom corner.
St Mirren continued to throw men forward in the closing minutes but a superb block from Ryan O’Leary denied Imrie in injury-time and Kilmarnock held out for a second successive home win in the Clydesdale Bank Premier League.